app/testpmd: add timeout in Rx queue flushing

app/testpmd: add timeout in Rx queue flushing

Testpmd can stuck inside do while loop of the flush_fwd_rx_queues()
function. As non-zero packets are returned always by rte_eth_rx_burst()
function when compiled with no optimizations and if input line rate is
high. "do while" loop must exit at one stage to proceed further to
enable packet forwarding and forward the packets. So timer is set to
exit the do while loop after 1 second.

Fixes: af75078f ("first public release")

Signed-off-by: Reshma Pattan <reshma.pattan@intel.com>
Acked-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>