UPDATE: MPLS: if_mpe(4): refactoring

I've removed /usr/src/sbin/ifconfig/ifmpe.c, because
this was a redundancy (and this redundancy was wrong
and a blatant flaw)!!!

BTW, af_mpls.c modefied, but implementation contains
flaws (causes coredump)... if user tries to bind
instance of if_mpe(4) with network interface for
by if_mpe(4) proxyfied transmission.

I'll fix this stuff as quick as possible!!!