smb: smbdirect: introduce smbdirect_connection_reassembly_{append,first}_recv_io()

smb: smbdirect: introduce smbdirect_connection_reassembly_{append,first}_recv_io()

These are basically copies of enqueue_reassembly() and
[_]get_first_reassembly() of both client and server. The only difference
is that enqueue_reassembly() of the server does not have:
sc->statistics.enqueue_reassembly_queue++

Also smbdirect_connection_reassembly_first_recv_io() makes use of
list_first_entry_or_null() in order to simplify the code.

In the next commits they will replace the existing functions.

Cc: Steve French <smfrench@gmail.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Long Li <longli@microsoft.com>
Cc: Namjae Jeon <linkinjeon@kernel.org>
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>