RDMA/iwcm: Allow AFONLY binding for IPv6 addresses

Binding IPv6 address/port to AF_INET6 domain only is provided via
rdma_set_afonly(), but was not signalled to the provider.  Applications
like NFS/RDMA bind the same port to both IPv4 and IPv6 addresses
simultaneously and thus rely on it working correctly.

Link: https://lore.kernel.org/r/20210219143441.1068-1-bmt@zurich.ibm.com
Tested-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Bernard Metzler <bmt@zurich.ibm.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>