Remove redundant linux/version.h includes from net/

Remove redundant linux/version.h includes from net/

It was suggested by "make versioncheck" that the follwing includes of
linux/version.h are redundant:

  /home/jj/src/linux-2.6/net/caif/caif_dev.c: 14 linux/version.h not needed.
  /home/jj/src/linux-2.6/net/caif/chnl_net.c: 10 linux/version.h not needed.
  /home/jj/src/linux-2.6/net/ipv4/gre.c: 19 linux/version.h not needed.
  /home/jj/src/linux-2.6/net/netfilter/ipset/ip_set_core.c: 20 linux/version.h not needed.
  /home/jj/src/linux-2.6/net/netfilter/xt_set.c: 16 linux/version.h not needed.

and it seems that it is right.

Beyond manually inspecting the source files I also did a few build
tests with various configs to confirm that including the header in
those files is indeed not needed.

Here's a patch to remove the pointless includes.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Acked-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>