mlxsw: spectrum_flower: Do not stop at FLOW_ACTION_VLAN_MANGLE

The handler for FLOW_ACTION_VLAN_MANGLE ends by returning whatever the
lower-level function that it calls returns. If there are more actions lined
up after this action, those are never offloaded. Fix by only bailing out
when the called function returns an error.

Fixes: a150201a

 ("mlxsw: spectrum: Add support for vlan modify TC action")
Signed-off-by: Petr Machata <petrm@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>