[ Upstream commit 59f997b088d26a774958cb7b17b0763cd82de7ec ]

A MAC address must be unique among all the macvlan devices with the same
lower device. The only exception is the passthru [sic] mode,
which shares the lower device address.

When duplicate addresses are detected, EBUSY is returned when bringing
the interface up:

    # ip link add macvlan0 link eth0 type macvlan
    # read addr </sys/class/net/eth0/address
    # ip link set macvlan0 address $addr
    # ip link set macvlan0 up
    RTNETLINK answers: Device or resource busy

Use correct error code which is EADDRINUSE, and do the check also
earlier, on address change:

    # ip link set macvlan0 address $addr
    RTNETLINK answers: Address already in use
Signed-off-by: NMatteo Croce <mcroce@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NSasha Levin <sashal@kernel.org>