net: Allow dependancies of FDDI & Tokenring to be modular.

I noticed it isn't possible to build token ring & fddi drivers
without causing LLC, and a bunch of other things to be forced
built-in.  For distro kernels, this means carrying a chunk of
code in the vmlinuz, even if the user doesn't use those protocols.

Signed-off-by: Dave Jones <davej@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>