Bugfixes. targeting route(8) and netmpls/mpls_rmx.c.

In function mpls_xconnect_fib() missing (forgotten) RTF_MPE enabled
in conjunction set RTF_PUSH operation. Defined RTF_MPE flag ensures
such that ingress MPLS label mapping is valid. Otherwise, by ip_output()
generated PDU in FEC maps to granular MPLS ingress label won't be tagged
by out-seg.
	Revision of MPLS related implementation of route(8), Further, I've
introduced K_STACK command maps to RTF_STACKING.
	Let be FEC denotes set containing Forward Equivalence
Classes and LSP denotes set denotes MPLS label space.
    Commands K_[POP|PUSH] in K may applied either by route(8)

 (a) [add|delete] fec -[pop|push] seg

where seg = seg_in = seg_out or by

 (b) [add|delete] fec -[stack] seg_in -[pop|push|swap] seg_out

if seg_in not equals seg_out. Swap operation will be applied by

 (c) [add|delete] fec -[swap] seg_in -[mpls] seg_out

seperately.
	Some bugfixes applies to mpls_xconnect_fib() in netmpls/mpls_rmx.c.