selftests: netdevsim: Increase sleep time in hw_stats_l3.sh test

hw_stats_l3.sh test is failing often for l3 stats shows less than 20
packets after 2 seconds sleep.

This is happening since there is a race between the 2 seconds sleep and
the netdevsim actually delivering the packets.

Increase the sleep time so the packets will be delivered successfully on
time.

Signed-off-by: Danielle Ratson <[e-mail]>
Reviewed-by: Petr Machata <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

tools/testing/selftests/drivers/net/netdevsim/hw_stats_l3.sh

···
 	((pkts < 10))
 	check_err $? "$type stats show >= 10 packets after first enablement"
 
-	sleep 2
+	sleep 2.5
 
 	local pkts=$(get_hwstat dummy1 l3 rx.packets)
 	((pkts >= 20))
-	check_err $? "$type stats show < 20 packets after 2s passed"
+	check_err $? "$type stats show < 20 packets after 2.5s passed"
 
 	$IP stats set dev dummy1 ${type}_stats off