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

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

Add flush support to match entries with or without (if "no" is
prepended) sticky flag.

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

$ bridge fdb flush dev br0 nosticky
This will delete all entries except the ones with sticky flag in
br0's fdb table.

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