net: dsa: add port STP state helper

Add a void helper to set the STP state of a port, checking first if the
required routine is provided by the driver.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
1 file changed