t_n_rows (n_rows before) has to be local for table. Having it global sometimes
caused to print wrong number of rows in tables. This bug may even cause snmpd
to crash.
It was dependent on the call order of *_data_fill funtions.

Change the n_rows into t_n_rows, since the usage of n_rows variable is common
in the snmp code. By this avoid potential errors like variable overleaping
problems.

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