net: dsa: rtl8366: Check validity of passed VLANs

The rtl8366_set_vlan() and rtl8366_set_pvid() get invalid
VLANs tossed at it, especially VLAN0, something the hardware
and driver cannot handle. Check validity and bail out like
we do in the other callbacks.

Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>