smb: server: inline smb_direct_create_header() into smb_direct_post_send_data()

smb: server: inline smb_direct_create_header() into smb_direct_post_send_data()

The point is that ib_dma_map_single() is done first, but
the 'Fill in the packet header' will be done after
smbdirect_map_sges_from_iter().

This will simplify further changes in order to
share common code with the client.

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>