It looks like the lldp protocol (openlldp) triggers the below error when the system has a carp interface:

..
carp_looutput: af=1 unexpected
carp_looutput: af=1 unexpected
carp_looutput: af=1 unexpected
..

Investigating a little bit I've found this in /usr/src/sys/net/netinet/ip_carp.c:

carp_looutput(struct ifnet *ifp, struct mbuf *m, struct sockaddr *dst,
    struct route *ro)
{
..
#if 1   /* XXX */
        switch (dst->sa_family) {
        case AF_INET:
        case AF_INET6:
        case AF_IPX:
        case AF_APPLETALK:
                break;
        default:
                printf("carp_looutput: af=%d unexpected\n", dst->sa_family);
                m_freem(m);
                return (EAFNOSUPPORT);
        }
..
}

It looks like the switch (dst->sa_family) is returning 1 (dmesg log says: carp_looutput: af=1 unexpected). 

I thought I could just ignore this (and comment the printf out, but after some hours lldp consumes a bunch of swap and eventually dies:

..
swap_pager_getswapspace(2): failed
swap_pager_getswapspace(16): failed
pid 2628 (lldpd), uid 0, was killed: out of swap space

I wonder if ip_carp.c, when checking the address_family was not supposed to  accomodate the lldp packages.

How-To-Repeat: 1- Create a carp interface, no peer required, any ip address
2- Install and install openlldp
3- Follow up dmesg and logs