bridge: Add internal flags for per-{Port, VLAN} neighbor suppression

Add two internal flags that will be used to enable / disable per-{Port,
VLAN} neighbor suppression:

1. 'BR_NEIGH_VLAN_SUPPRESS': A per-port flag used to indicate that
per-{Port, VLAN} neighbor suppression is enabled on the bridge port.
When set, 'BR_NEIGH_SUPPRESS' has no effect.

2. 'BR_VLFLAG_NEIGH_SUPPRESS_ENABLED': A per-VLAN flag used to indicate
that neighbor suppression is enabled on the given VLAN.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: David S. Miller <davem@davemloft.net>