s3:smb2_server: reset req->last_session_id and req->last_tid after using it

s3:smb2_server: reset req->last_session_id and req->last_tid after using it

If we can find a valid session or tcon we'll set it after the lookup,
but it need to make sure to reset it if we don't find the session.

This fixes a problem where a compound unrelated request between
related requests doesn't reset the session.

If we have 3 requests in a compound chain, request 3 should never
use the id's cached from request 1. It should only every inherit
handles from request 2.

metze
(similar to commit 2552b6632372b35cbd7b788c4e00091dfe520a41)

Signed-off-by: Stefan Metzmacher <metze@samba.org>