s4:torture/smb2: add smb2.bench.echo

s4:torture/smb2: add smb2.bench.echo

This test calls SMB2_Echo in a loop per connection.

For 4 connections with 2 parallel loops use this:

time smbtorture //127.0.0.1/m -Uroot%test smb2.bench.echo \
	--option="torture:timelimit=600" \
	--option="torture:nprocs=1" \
	--option="torture:qdepth=2"

Sometimes the bottleneck is the smbtorture process.
In order to bring the smbd process to 100% cpu, you can use
'--option="libsmb:client_guid=6112f7d3-9528-4a2a-8861-0ca129aae6c4"'
and run multiple instances of the test at the same time,
which both talk to the same smbd process.

This is a very useful test to show how many requests are possible
at the raw SMB2 layer.

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Thu Aug 11 19:23:37 UTC 2022 on sn-devel-184