cifsd: Select SG_POOL for SMB_SERVER_SMBDIRECT

hulk-robot following build error:
 fs/cifsd/transport_rdma.c: In function 'read_write_done':
 fs/cifsd/transport_rdma.c:1297:2: error: implicit declaration of
function 'sg_free_table_chained'
[-Werror=implicit-function-declaration]
  1297 |  sg_free_table_chained(&msg->sgt, SG_CHUNK_SIZE);

The reason is CONFIG_SG_POOL is not enabled in the config, to
avoid such failure, select SG_POOL in Kconfig for SMB_SERVER_SMBDIRECT.
Signed-off-by: Zhang Xiaoxu <zhangxiaoxu5@huawei.com>
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifsd/Kconfig

@@ -43,6 +43,7 @@ config SMB_SERVER
 config SMB_SERVER_SMBDIRECT
 	bool "Support for SMB Direct protocol"
 	depends on SMB_SERVER=m && INFINIBAND && INFINIBAND_ADDR_TRANS || SMB_SERVER=y && INFINIBAND=y && INFINIBAND_ADDR_TRANS=y
+	select SG_POOL
 	default n
 
 	help