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

Add flush support to match static or non-static entries if "no" is
prepended respectively. Note that static entries are only NUD_NOARP ones
without NUD_PERMANENT, also when matching non-static entries exclude
permanent entries as well (permanent entries by definition are also
static).

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

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

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