Bug 160295

The -P argument to ypserv breaks NIS over TCP.  After starting
ypserv -P 666 I see:

tcp4       0      0 *.666                  *.*                    CLOSED

From the code ( http://svnweb.freebsd.org/base/stable/7/usr.sbin/ypserv/yp_main.c?r1=172506&r2=177753 )
the problem is rather obvious: the sock variable is used for both the
udp and tcp sockets, and so while transp = svcudp_create(sock); works
fine (after losing the tcp socket), transp = svctcp_create(sock, 0, 0);
doesn't work at all on the already open udp socket.

Here are the relevant calls.  Notice fd 4 is never touched again:
socket(PF_INET,SOCK_STREAM,0)                    = 4 (0x4)
bind(4,{ AF_INET 0.0.0.0:666 },16)               = 0 (0x0)
socket(PF_INET,SOCK_DGRAM,0)                     = 5 (0x5)
bind(5,{ AF_INET 0.0.0.0:666 },16)               = 0 (0x0)
getsockopt(0x5,0x0,0x13,0x7fffffffe4ec,0x7fffffffe4e0,0x7fffffffe340) = 0 (0x0)
setsockopt(0x5,0x0,0x13,0x7fffffffe4e8,0x4,0x7fffffffe458) = 0 (0x0)
bind(5,{ AF_INET 0.0.0.0:0 },16)                 ERR#22 'Invalid argument'
setsockopt(0x5,0x0,0x13,0x7fffffffe4ec,0x4,0x7fffffffe458) = 0 (0x0)
listen(0x5,0x80,0x13,0x8007dd42c,0xffffff80ec8b4d40,0x7fffffffe458) ERR#45 'Operation not supported'
getsockopt(0x5,0x0,0x13,0x7fffffffe4ec,0x7fffffffe4e0,0x800a00728) = 0 (0x0)
setsockopt(0x5,0x0,0x13,0x7fffffffe4e8,0x4,0x7fffffffe458) = 0 (0x0)
bind(5,{ AF_INET 0.0.0.0:0 },16)                 ERR#22 'Invalid argument'
setsockopt(0x5,0x0,0x13,0x7fffffffe4ec,0x4,0x7fffffffe458) = 0 (0x0)
listen(0x5,0x80,0x13,0x8007dd42c,0xffffff80ec8b4d40,0x7fffffffe458) ERR#45 'Operation not supported'

Fix: 

Use a different variable for each socket.
How-To-Repeat: Run ypserv -P <port>
Perform TCP NIS request from client