ar8216: set the pvid based on runtime state instead of port number to fix learning with enable_vlan = 0

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42753 3c298f89-4303-0410-b956-a3cf2f4a3e73