LU-15190 ptlrpc: fix duplication check

LU-15190 ptlrpc: fix duplication check

ptlrpc_server_check_for_resend() skips duplication check if
current exp_rpc_count == 0 which is wrong as exp_rpc_count
is incremented for RPCs in progress.

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: I4ba1600341d916871f66aceb4d6a1043dd015e55
Reviewed-on: https://review.whamcloud.com/45445
Reviewed-by: Mike Pershin <mpershin@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>