net/smc: mark optional smcd_ops and check for support when called

Some operations are not supported by new introduced Emulated-ISM, so
mark them as optional and check if the device supports them when called.

Signed-off-by: Wen Gu <guwen@linux.alibaba.com>
Reviewed-by: Wenjia Zhang <wenjia@linux.ibm.com>
Reviewed-and-tested-by: Jan Karcher <jaka@linux.ibm.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>