kernel: generic: Fix skip GRO for foreign MAC address patches

Somewhere in the kernel 4.9 migration process it looks like this patch
was broken. The update should be done when a device is added to the
bridge and when it gets removed, currently it is only done on the remove
path twice which does not make any sense.
I do not have a setup to test this now so this is only compile tested.

Fixes: f791fb4a ("kernel: add linux 4.9 support")
Fixes: b3f95490 ("kernel: generic: Add kernel 4.14 support")
Reported-by: Andrey Jr. Melnikov <temnota.am@gmail.com>
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>