Misc. bugfixes. route(8) and netmpls/mpls_rmx.c.

Handling of gateway in rt_addrinfo{} by route(8) and netmpls/mpls_rmx.c
changed. Segements for x-connect are encoded by sockaddr_mpls{} maps to
sockaddr_ftn{}, where in-seg is stored by

 (a) satosmpls(dst)->smpls_label = ...

and out-seg by

 (b) satosftn(dst)->sftn_label = ...

If fec will be removed, call of mpls_link_rtrequest removes all
corrosponding MPLS lanel biding automatically.

Function mpls_rt_setgate deprecated and its codesection merged with
mpls_rt_output_fib.

Misc. bugfixes in netmpls/mpls_arp.c.