lcs: fix compilation for !CONFIG_IP_MULTICAST

drivers/s390/net/lcs.c: In function 'lcs_new_device':
drivers/s390/net/lcs.c:2179: error: implicit declaration of function 'lcs_set_multicast_list'

Reported-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Ursula Braun <ursula.braun@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>