First pass at 3.15 import

@bbonev: took your advice and took as stab at the merge/update. It builds, and violently crashes when assigning an IP to a new interface (though the interface is created without issue).
Could you please review the changes and point me to where it is i screwed up? This seems worth pursuing and getting it pushed upstream if possible, but it seems we're both pretty time constrained so i'm hoping we can split up the load to get this running.

----

DO NOT USE OUTSIDE OF TEST ENVIRONMENTS - this is dangerous code,
it will eat your stuff, spill your coffee, and crash your kernel.

Initial import of eoip.c, gre_demux, and related build patches.
Replace __IPTUNNEL_XMIT, add the GRE counters to gre_demux, and
cosmetics.

It builds, and seems to create the initial EoIP tunnel adapter.
Setting an IP address causes hard locks and panic.