Add support for creating a MACVLAN interface in "source" mode by
specifying Mode=source in the [MACVLAN] section of a .netdev file.
A list of allowed MAC addresses for the corresponding MACVLAN can also
be specified with the SourceMACAddress= option of the [MACVLAN] section.
An example .netdev file:
[NetDev]
Name=macvlan0
Kind=macvlan
MACAddress=02:DE:AD:BE:EF:00
[MACVLAN]
Mode=source
SourceMACAddress=02:AB:AB:AB:AB:01 02:CD:CD:CD:CD:01
SourceMACAddress=02:EF:EF:EF:EF:01
The same keys can also be specified in [MACVTAP] for MACVTAP kinds of
interfaces, with the same semantics.