Make the ti_padstate_devmap arrays ststic, they are only used with the
file where they are defined.
Overhaul if_gif(4):
 o convert to if_transmit;
 o use rmlock to protect access to gif_softc;
 o use sx lock to protect from concurrent ioctls;
 o remove a lot of unneeded and duplicated code;
 o remove cached route support (it won't work with concurrent io);
 o style fixes.

Reviewed by:	melifaro
Obtained from:	Yandex LLC
MFC after:	1 month
Sponsored by:	Yandex LLC