Initialize a variable in sys/contrib/ipfilter/netinet/ip_tftp_pxy.c, to
silence a gcc warning.

Approved by:	re (rodrigc)
X-MFC-With:	r255332
Add support for "vnet jname" argument in ifconfig_IF.  The vnet keyword
is ignored except for "rc.d/netif vnet{up,down} ifn" because a jail is
usually created after interface initialization on boot time.

"rc.d/netif vnetup ifn" moves ifn into the specified jail.  It is
designed to be used in other scripts like rc.d/jail, not automatically
invoked during the interface initialization.

Approved by:	re (kib)