smb: server: make use of functions from smbdirect_rw.c

smb: server: make use of functions from smbdirect_rw.c

The copied code only got new names, some indentation/formatting changes,
some variable names are changed too.

They also only use struct smbdirect_socket instead of
struct smb_direct_transport.

But the logic is still the same.

Cc: Namjae Jeon <linkinjeon@kernel.org>
Cc: Steve French <smfrench@gmail.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: linux-cifs@vger.kernel.org
Cc: samba-technical@lists.samba.org
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>