In the legacy RX descriptor mode, VLAN tag was saved to d->special
by e1000e_build_rx_metadata() in e1000e_write_lgcy_rx_descr(), but
it was then zeroed out again at the end of the call, which is wrong.

Fixes: c89d416a ("e1000e: Don't zero out buffer address in rx descriptor")
Reported-by: Markus Carlstedt <markus.carlstedt@windriver.com>
Signed-off-by: Christina Wang <christina.wang@windriver.com>
Signed-off-by: Bin Meng <bin.meng@windriver.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>