bonding:record primary when modify it via sysfs

If we modify primary via sysfs and it is not a valid slave,
we should record it for future use, and this behavior is the same with
bond_check_params().

Signed-off-by: Weiping Pan <wpan@redhat.com>
Acked-by: Nicolas de Pesloüan <nicolas.2p.debian@free.fr>
Signed-off-by: Jay Vosburgh <fubar@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>