Stop setting the default route to the IP of the interface itself when the

Stop setting the default route to the IP of the interface itself when the
bootp/dhcp server doesn't provide a router option.  Doing so prevents
setting defaultrouter=<ip> in rc.conf (it fails because there's already
a bogus default route installed by bootpc_init).

When an admin wants to use this style of proxy arp on an interface, the
proper mechanism is to set the "use-lease-addr-for-default-route" flag
in the dhcp server config.  That causes the lease address to be delivered
in the routers option, and the normal handling of the routers option will
then install the self-ip as the default route.

PR:		187094