smb: server: Use common error handling code in smb_direct_rdma_xmit()

Add two jump targets so that a bit of exception handling can be better
reused at the end of this function implementation.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>