bridge: add support for VLAN filtering

bridge: add support for VLAN filtering

VLANs can be defined using bridge-vlan sections, like the following example:

config bridge-vlan
	option device 'switch0'
	option vlan '1'
	option ports "lan1 lan2 lan3 lan4:t*"

Each member port can be confgured with optional attributes after ':'
 - t: member port is tagged
 - *: This is the primary VLAN for the port (PVID)

VLAN member interfaces are automatically added as bridge members

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