net: bridge: fdb: add support for flush filtering based on ndm flags and state

Add support for fdb flush filtering based on ndm flags and state. NDM
state and flags are mapped to bridge-specific flags and matched
according to the specified masks. NTF_USE is used to represent
added_by_user flag since it sets it on fdb add and we don't have a 1:1
mapping for it. Only allowed bits can be set, NTF_SELF and NTF_MASTER are
ignored.

Signed-off-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: David S. Miller <davem@davemloft.net>