Notable changes:
* Fixes PR 34268.
* Separates the code from gif(4) (which is more cleaner).
* Allows the usage of STP (Spanning Tree Protocol).
* Removed EtherIP implementation from gif(4)/tap(4).
Some input from Christos.
Hans Rosenfeld (rosenfeld at grumpf.hope-2000.org)
This change makes it possible to add gif interfaces to bridges, which
will then send and receive IP protocol 97 packets. Packets are Ethernet
frames with an EtherIP header prepended.
to protocol handlers, based on src/dst (for ip proto #4/41).
see comment in ip_encap.c for details of the problem we have.
there are too many protocol specs for ip proto #4/41.
backward compatibility with MROUTING case is now provided in ip_encap.c.
fix ipip to work with gif (using ip_encap.c). sorry for breakage.
gif now uses ip_encap.c.
introduce stf pseudo interface (implements 6to4, another IPv6-over-IPv4 code
with ip proto #41).