UPDATE: MPLS: if_mpe(4): refactoring, status report

Some bugs terminated due to ifconfig(8) and reintegration
into MPLS stack. BTW, due to unfinished refactoring, if_mpe(4)
does not work properly, e. g. MPLS ingress label assignement,
network interface mapping (due to SIOCSIFPHYS SPI), and other
unfinished work (relating if_mpe(4)).

This commit might be understood as status report to show
progress. BTW, I'll resolve this issue as quick as possible,
be patient... :-)