macvlan: validate setting of multiple remote source MAC addresses

Remote source MAC addresses can be set on a 'source mode' macvlan
interface via the IFLA_MACVLAN_MACADDR_DATA attribute. This commit
tightens the validation of these MAC addresses to match the validation
already performed when setting or adding a single MAC address via the
IFLA_MACVLAN_MACADDR attribute.

iproute2 uses IFLA_MACVLAN_MACADDR_DATA for its 'macvlan macaddr set'
command, and IFLA_MACVLAN_MACADDR for its 'macvlan macaddr add' command,
which demonstrates the inconsistent behaviour that this commit
addresses:

 # ip link add link eth0 name macvlan0 type macvlan mode source
 # ip link set link dev macvlan0 type macvlan macaddr add 01:00:00:00:00:00
 RTNETLINK answers: Cannot assign requested address
 # ip link set link dev macvlan0 type macvlan macaddr set 01:00:00:00:00:00
 # ip -d link show macvlan0
 5: macvlan0@eth0: <BROADCAST,MULTICAST,DYNAMIC,UP,LOWER_UP> mtu 1500 ...
     link/ether 2e:ac:fd:2d:69:f8 brd ff:ff:ff:ff:ff:ff promiscuity 0
     macvlan mode source remotes (1) 01:00:00:00:00:00 numtxqueues 1 ...

With this change, the 'set' command will (rightly) fail in the same way
as the 'add' command.

Signed-off-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>