s3:libsmb: fix smb signing for fragmented trans/trans2/nttrans requests

s3:libsmb: fix smb signing for fragmented trans/trans2/nttrans requests

Before we send the secondary requests we need to remove the
old mid=>seqnum mapping and reset cli->mid and make the new
mid=>seqnum mapping "persistent".

The bug we had in cli_send_trans was this:
The first cli_send_smb() incremented cli->mid
and the secondary requests used the incremented mid,
but as cli->outbuf still had the correct mid,
we send the correct mid to the server. The real problem
was that the cli_send_smb() function stored the seqnum
under the wrong mid.

cli_send_nttrans() was totally broken and now follows the
same logic as cli_send_trans().

The good thing is that in practice the problem is unlikely to happen,
because max_xmit is large enough to avoid secondary requests.

metze
(cherry picked from commit 880fbc4e8cd67de73c4bcda94489eb1e1422a04b)