Pull up following revision(s) (requested by knahakara in ticket #303):
sys/net/if_gif.c: 1.129-1.130
sys/net/if_gif.h: 1.26-1.27
sys/netinet/in_gif.c: 1.88
sys/netinet6/in6_gif.c: 1.86
add lock for percpu route like l2tp(4).
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add lock for sclist to exclude ifconfig gifX add/delete and ifconfig gifX tunnel
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update locking notes.

(snj)