xpcs_config() has 'advertising' input that is required for C37 1000BASE-X
AN in later patch series. So, we prepare xpcs_do_config() for it.

For sja1105, xpcs_do_config() is used for xpcs configuration without
depending on advertising input, so set to NULL.
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Ong Boon Leong <boon.leong.ong@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>