ibmvnic: fix ibmvnic_set_mac

ibmvnic: fix ibmvnic_set_mac

Jakub Kicinski brought up a concern in ibmvnic_set_mac().
ibmvnic_set_mac() does this:

	ether_addr_copy(adapter->mac_addr, addr->sa_data);
	if (adapter->state != VNIC_PROBED)
		rc = __ibmvnic_set_mac(netdev, addr->sa_data);

So if state == VNIC_PROBED, the user can assign an invalid address to
adapter->mac_addr, and ibmvnic_set_mac() will still return 0.

The fix is to validate ethernet address at the beginning of
ibmvnic_set_mac(), and move the ether_addr_copy to
the case of "adapter->state != VNIC_PROBED".

Fixes: c26eba03e407 ("ibmvnic: Update reset infrastructure to support tunable parameters")
Signed-off-by: Lijun Pan <ljp@linux.ibm.com>
Link: https://lore.kernel.org/r/20201027220456.71450-1-ljp@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>