simple/rdm_cntr_pingpong: Fix race condition

If a message arrived before fi_cntr_read is called, then the threshold argument for fi_cntr_wait
would not be correct. Replace it with a recv_outs variable that tracks the # of outstanding recvs.

Signed-off-by: Arun C Ilango <arun.ilango@intel.com>
Merge pull request #99 from a-ilango/dev

simple/rdm_cntr_pingpong: Fix race condition