bridge: create utility funcs for BridgeVlanAdd for PVID and Trunk

[glimchb]

for example in https://github.com/opiproject/opi-evpn-bridge/blob/main/pkg/utils/netlink.go add :

// BridgePVIDVlanAdd configure port VLAN id for link
func BridgePVIDVlanAdd(nlink Netlink, link netlink.Link, vlanID int) error {
	// pvid, egress untagged
	return nlink.BridgeVlanAdd(link, uint16(vlanID), true, true, false, true)
}

// BridgeTrunkVlanAdd configure vlan trunk on link
func BridgeTrunkVlanAdd(nlink Netlink, link netlink.Link, vlans []int) error {
	// egress tagged
	for _, vlanID := range vlans {
		if err := nlink.BridgeVlanAdd(link, uint16(vlanID), false, false, false, true); err != nil {
			return err
		}
	}
	return nil
}

because this is hard to read

opi-evpn-bridge/pkg/evpn/port.go

Line 101 in 2cfcb29

if err := netlink.BridgeVlanAdd(iface, vid, true, true, false, false); err != nil {

:

netlink.BridgeVlanAdd(iface, vid, true, true, false, false)