Add ZC support for igc adapters (Intel 2.5 Gbit)

[cardigliano]

Is is requested to add support for i225 adapters (Intel 2.5 Gbit),
however there is no out-of-tree igc driver currently available from Intel to be patch'ed with ZC support,
thus it is hard to develop and maintain such a drivers for all kernels.

https://sourceforge.net/p/e1000/mailman/message/37392510/