There was a special case when there was no update of pstats, but status was
recalculated. Since counters were not updated then deltas of counters were
within limits. It could happen that counters are growing, but statuses are
returning "ok".

For example problem was in the case, when object wrsPstatsHCRXDropRTUFull.1 was
increasing at every read:
$ snmpget WR-SWITCH-MIB::wrsPortStatusSfpError.1 # this triggers a read of
status ports
$ sleep 2
WR-SWITCH-MIB::wrsPortStatusSfpError.1 = INTEGER: sfpOk(1)
$ snmpget WR-SWITCH-MIB::wrsRTUStatus.0 # triggers only read of pstats, values
of status ports are cached (only 2 seconds elapsed)
WR-SWITCH-MIB::wrsRTUStatus.0 = INTEGER: error(2)
$ sleep 4
$ snmpget WR-SWITCH-MIB::wrsRTUStatus.0 # pstats value are cached, but deltas
are re-calculated and are equal to 0. This sould report error as well.
WR-SWITCH-MIB::wrsRTUStatus.0 = INTEGER: ok(1)
After the code is fixed the last one returns error(2)

Signed-off-by: Adam Wujek <adam.wujek@cern.ch>