UPDATE: MPLS and if_bridge(4): bugfixes, status report ...
Several bugfixes and comments are changed. Further, code
sections due to PPPOE_PROXY "feature" removed completely.

At the moment, I'm working to fix several bugs due to
OSI-L2/VPN... I'll commit changes as quick as possible.

Further, I'm refactoring if_mpe(4) at this moment!!!
I've removed /usr/src/sbin/ifconfig/ifmpe.c, because
this was a redundancy (and this redundancy was wrong
and a blatant flaw)!!!