Use atomic inc for new_clientid and new_clientid_verifier

Also correct function name for new_clientid_verifier.

Ported from 1.5.x: 5f67b48645e840c4d502eec440d7e0c3fe26d647

Signed-off-by: Frank Filz <ffilz@us.ibm.com>
Signed-off-by: Allison Henderson <achender@vnet.linux.ibm.com>