With a routing daemon like quagga running, doing a kldload of a network driver causes a panic. I was testing with if_cxgb but it seems any network driver will do (I confirmed with if_igb as well).

11.0-STABLE FreeBSD 11.0-STABLE #1 r311283: Wed Jan  4 14:04:02 EST 2017 amd64

with a few static ipv4 and ipv6 routes in zebra.conf, with zebra running, I do a kldload if_cxgb and the box panics with

cxgbc0: <Chelsio T310, 1 port> mem
0xf7081000-0xf7081fff,0xf6800000-0xf6ffffff,0xf7080000-0xf7080fff irq 16
at device 0.0 on pci5
cxgbc0: PCIe x4 Link, expect reduced performance
cxgbc0: using MSI-X interrupts (5 vectors)
cxgbc0: firmware needs to be updated to version 7.11.0
cJan  4 13:03:02 xgbc0: Firmware Version 5.0.0
cxgb0: <Port 0 10GBASE-SR> on cxgbc0
cxgb0: Using defaults for TSO: 65518/35/2048
cxgb0:
Ethernet address: 00:07:43:07:9e:14

kernel:Fatal trap 12: page fault while in kernel mode
c found old FW mipuinor version(5.0)d =, driver compile 2; d for version
7.apic11
 id = 04
fault virtual address   = 0x0
fault code              = supervisor read instruction, page not present
instruction pointer     = 0x20:0x0
stack pointer           = 0x28:0xfffffe085d2df728
frame pointer           = 0x28:0xfffffe085d2df750
code segment            = base rx0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, long 1, def32 0, gran 1
processor eflags        = interrupt enabled, resume, IOPL = 0
current process         = 420 (zebra)
trap number             = 12
panic: page fault
cpuid = 0
KDB: stack backtrace:
#0 0xffffffff806fe447 at kdb_backtrace+0x67
#1 0xffffffff806b4966 at vpanic+0x186
#2 0xffffffff806b47d3 at panic+0x43
#3 0xffffffff80997f82 at trap_fatal+0x322
#4 0xffffffff8099814c at trap_pfault+0x1bc
#5 0xffffffff80997800 at trap+0x280
#6 0xffffffff8097c411 at calltrap+0x8
#7 0xffffffff807b90fd at ifioctl+0x6dd
#8 0xffffffff8071c1d6 at kern_ioctl+0x346
#9 0xffffffff8071bddf at sys_ioctl+0x13f
#10 0xffffffff8099890e at amd64_syscall+0x50e
#11 0xffffffff8097c6fb at Xfast_syscall+0xfb
Uptime: 3m9s
Dumping 1635 out of 32675
MB:..1%..11%..21%..31%..41%..51%..61%..71%..81%..91%

With igb

igb0: <Intel(R) PRO/1000 Network Connection, Version - 2.5.3-k> port
0xc000-0xc01f mem 0xf7200000-0xf727ffff,0xf7280000-0xf7283fff irq 17 at
device 0.0 on pci4
igb0: Using MSIX interrupts with 5 vectors
igb0:
Ethernet address: 00:25:90:47:b5:d8

Fatal trap 12: page fault while in kernel mode
cpuid = 3; apic id = 06
fault virtual address   = 0x0
fault code              = supervisor read instruction, page not present
instruction pointer     = 0x20:0x0
stack pointer           = 0x28:0xfffffe085d4d1728
frame pointer           = 0x28:0xfffffe085d4d1750
igb0: code segment              = base rx0, limit 0xfffff, type 0x1b
Bound queue 0 to cpu 0
                        = DPL 0, pres 1, long 1, def32 0, gran 1
processor eflags        = interrupt enabled, resume, IOPL = 0
current process         = 846 (zebra)
trap number             = 12
panic: page fault
cpuid = 3
KDB: stack backtrace:
#0 0xffffffff806efae7 at kdb_backtrace+0x67
#1 0xffffffff806a6006 at vpanic+0x186
#2 0xffffffff806a5e73 at panic+0x43
#3 0xffffffff80989622 at trap_fatal+0x322
#4 0xffffffff809897ec at trap_pfault+0x1bc
#5 0xffffffff80988ea0 at trap+0x280
#6 0xffffffff8096dab1 at calltrap+0x8
#7 0xffffffff807aa79d at ifioctl+0x6dd
#8 0xffffffff8070d876 at kern_ioctl+0x346
#9 0xffffffff8070d47f at sys_ioctl+0x13f
#10 0xffffffff80989fae at amd64_syscall+0x50e
#11 0xffffffff8096dd9b at Xfast_syscall+0xfb
Uptime: 1m9s
Dumping 1267 out of 32675
MB:..2%..11%..21%..31%..41%..51%..61%..71%..81%..91%
Dump complete


kgdb)  l *(ifioctl+0x6dd)
0xffffffff807b90fd is in ifioctl (/usr/src/sys/net/if.c:2655).
2650            case SIOCGIFMEDIA:
2651            case SIOCGIFXMEDIA:
2652            case SIOCGIFGENERIC:
2653                    if (ifp->if_ioctl == NULL)
2654                            return (EOPNOTSUPP);
2655                    error = (*ifp->if_ioctl)(ifp, cmd, data);
2656                    break;
2657
2658            case SIOCSIFLLADDR:
2659                    error = priv_check(td, PRIV_NET_SETLLADDR);
Current language:  auto; currently minimal
(kgdb)

Some discussion at 
https://lists.freebsd.org/pipermail/freebsd-stable/2017-January/086562.html