mlxsw: spectrum: Add extack for VLAN enslavements

Similar to physical ports, enslavement of VLAN devices can also fail.
Use extack to indicate why the enslavement failed.

$ ip link add link enp1s0np1 name enp1s0np1.10 type vlan id 10
$ ip link add name bond0 type bond mode 802.3ad
$ ip link set dev enp1s0np1.10 master bond0
Error: spectrum: VLAN devices only support bridge and VRF uppers.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Acked-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>