net: Cavium: Fix MAC address setting in shutdown state

This bug pops up with NetworkManager on Fedora 21. NetworkManager tends to
stop the interface (nicvf_stop() is called) before changing settings. In
stopped state MAC cannot be sent to a PF. However, when the interface is
restarted (nicvf_open() is called), we ping the PF using NIC_MBOX_MSG_READY
message, and the PF replies back with old MAC address, overriding what we
had after MAC setting from userspace. As a result, we cannot set MAC
address using NetworkManager.

This patch introduces special tracking of MAC change in stopped state so
that the correct new MAC address is sent to a PF when interface is reopen.

Signed-off-by: Pavel Fedin <p.fedin@samsung.com>
Signed-off-by: David S. Miller <davem@davemloft.net>