This state field was never used, simply remained 0. Drop it from the
PCNetState and update the save/restore code accordingly, keeping
backward compatibility.

Patchworks-ID: 35314
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>