constants: add macvtap to interface type and name
compat: support macvtap interface type

Differentiate between using MACVLAN_/MACVTAP_ sysconfig variables.
ifconifg: add macvtap support
dbus: add macvtap service

Added new macvtap dbus services.
Augments existing macvlan code to handle new macvtap device type.
dbus: enable macvtap service
Merge pull request #201 from kmroz/macvtap-dev2-rc1

initial macvtap support