Add a new tunable "hw.bge.fake_autoneg", get rid of BGE_FAKE_AUTONEG kernel

Add a new tunable "hw.bge.fake_autoneg", get rid of BGE_FAKE_AUTONEG kernel
option.  This lets GENERIC kernel work with some broken "bge(4) + switch
modules" configurations.

By default this tunable is set to 0, if autonegociation breakage happens
for certain switch modules shipped with IBM/Intel blades, set this tunable
to 1.

Thank Devon H. O'Dell <devon.odell at gmail.com> for confirming this is
useful.

Initial-idea-from: hmp
Reminded-by: Devon H. O'Dell <devon.odell at gmail.com>