int alb_handle_addr_collision_on_attach (struct bonding * bond, struct slave * slave);
checks uniqueness of slave's mac address and handles the case the new slave uses the bonds mac address.
If the permanent hw address of slave is bond's hw address, we need to find a different hw address to give slave, that isn't in use by any other slave in the bond. This address must be, of course, one of the premanent addresses of the other slaves.
We go over the slave list, and for each slave there we compare its permanent hw address with the current address of all the other slaves. If no match was found, then we've found a slave with a permanent address that isn't used by any other slave in the bond, so we can assign it to slave.
this function is called before slave is attached to the bond slave list.
caller must hold the bond lock for write since the mac addresses are compared and may be swapped.