staging: lustre: ptlrpc: imp_peer_committed_transno should increase

imp_peer_committed_transno should not decrease as this can
confuse the users if imp_peer_committed_transno is used to
check commit status.

Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-7079
Reviewed-on: http://review.whamcloud.com/16161


Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: wangdi <di.wang@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>