imporve idle handling

Make idle handler send real messages if there are pending
real messages, as credits are piggibacked on real messages.

Currently comment out sending NOP for last one way messages
without receipt as the code was wrong and sent may irronious
NOP messages.

Kernel code is aligned with user space code as it rearms
the events only after doing polling, with the assumption that
during the work of the idle handler more messages will arive
which will eliminates the need to rearma the CQ event.

Signed-off-by: Shlomo Pongratz <shlomop@mellanox.com>