smbd: Fix channel sequence number checks for long-running requests

smbd: Fix channel sequence number checks for long-running requests

When the client's supplied csn overflows and hits a pending, long-running
request's csn, we panic. Fix this by counting the overflows in
smbXsrv_open_global0->channel_generation

Bug: https://bugzilla.samba.org/show_bug.cgi?id=13215

Pair-Programmed-With: Stefan Metzmacher <metze@samba.org>

Signed-off-by: Volker Lendecke <vl@samba.org>
Signed-off-by: Stefan Metzmacher <metze@samba.org>
(cherry picked from commit 0b57434151a8334a6e9b9b7542824ce4915421a2)