net: bridge: fdb: convert added_by_user to bitops

[ Upstream commit ac3ca6af ]

Straight-forward convert of the added_by_user field to bitops.

Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: bee2ef94 ("net: bridge: br_fdb_external_learn_add(): always set EXT_LEARN")
Signed-off-by: Sasha Levin <sashal@kernel.org>