vxlan: vxlan_core: Support FDB flushing by destination port

vxlan: vxlan_core: Support FDB flushing by destination port

Add support for flush VXLAN FDB entries by destination port. FDB entry
is stored as {MAC, SRC_VNI} + remote. The destination port is an attribute
of the remote. For multicast entries, the VXLAN driver stores a linked list
of remotes for a given key.

In user space, each remote is represented as a separate entry, so when
flush is sent with filter of 'destination port', flush only the match
remotes. In case that there are no additional remotes, destroy the entry.

For example, the following are stored as one entry with several remotes:
$ bridge fdb show dev vx10
00:00:00:00:00:00 dst 192.1.1.1 port 1111 vni 2000 self permanent
00:00:00:00:00:00 dst 192.1.1.1 port 1111 vni 3000 self permanent
00:00:00:00:00:00 dst 192.1.1.1 port 2222 vni 2000 self permanent
00:00:00:00:00:00 dst 192.1.1.1 vni 3000 self permanent

When user flush by port x, only the relevant remotes will be flushed:
$ bridge fdb flush dev vx10 port 1111

$ bridge fdb show dev vx10
00:00:00:00:00:00 dst 192.1.1.1 port 2222 vni 2000 self permanent
00:00:00:00:00:00 dst 192.1.1.1 vni 3000 self permanent

Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>