e1000: Add support for migrating the entire MAC registers' array

e1000: Add support for migrating the entire MAC registers' array

This patch makes the migration of the entire array of MAC registers
possible during live migration. The entire array is just 128 KB long, so
practically no penalty should be felt when transmitting it, additionally
to the previously transmitted individual registers. The advantage here is
eliminating the need to introduce new vmstate subsections in the future,
when additional MAC registers will be implemented.

Backward compatibility is preserved by introducing a e1000-specific
boolean parameter (in a later patch), which will be on by default.
Setting it to off would enable migration to older versions of QEMU.

Additionally, this parameter will be used to control the access to the
extra MAC registers in the future.

Signed-off-by: Leonid Bloch <leonid.bloch@ravellosystems.com>
Signed-off-by: Dmitry Fleytman <dmitry.fleytman@ravellosystems.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>