[SCSI] cnic: fix undefined reference to `ip6_route_output'

Fix cnic build for case of CONFIG_INET=n.
Fix cnic build for case of CONFIG_IPV6=m and CONFIG_CNIC=y.

Fixes these build errors:

cnic.c:(.text+0x236a1d): undefined reference to `ip_route_output_key'
cnic.c:(.text+0x15a8e8): undefined reference to `ip6_route_output'

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>