Added support for 'macvlan' link type to vlan connection profile

I recently ran into a situation where I wanted to create 'macvlan' type links with netctl and saw that the 'vlan' connection profile only supported the 'vlan' link type. I added code to choose and create either a 'vlan' or 'macvlan', similar to the 'tuntap' profile, to easily create these devices without using the 'custom' profile. Also a minor doc edit to the 'vlan' description where it seemed like the VLANID variable was optional but is not.