net: bridge: fdb: convert is_static to bitops

Convert the is_static to bitops, make use of the combined
test_and_set/clear_bit to simplify expressions in fdb_add_entry.

Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>