bridge: fdb: add flush [no]permanent entry matching

bridge: fdb: add flush [no]permanent entry matching

Add flush support to match permanent or non-permanent entries if "no" is
prepended respectively.

Examples:
$ bridge fdb flush dev br0 permanent
This will delete all permanent entries in br0's fdb table.

$ bridge fdb flush dev br0 nopermanent
This will delete all entries except the permanent ones in br0's fdb
table.

Signed-off-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: David Ahern <dsahern@kernel.org>