selftests: ovpn: reduce ping count in test.sh

selftests: ovpn: reduce ping count in test.sh

The second stage of test.sh ("run baseline data traffic") performs a
basic connectivity check with ping -qfc 500 -w 3.  On slower CI
instances this is too strict for TCP: the RTT is high enough that 500
echo requests do not reliably complete within 3 seconds, so the stage
flakes and the test fails even though the ovpn setup is healthy.

Reduce the packet count to 100 for both the plain and 3000-byte pings in
that stage.  This still verifies peer setup, key exchange, routing, and
data-path traffic, without making the basic connectivity check depend on
timing out under load.

Fixes: 959bc330a439 ("testing/selftests: add test tool and scripts for ovpn module")
Signed-off-by: Ralf Lici <ralf@mandelbit.com>
Signed-off-by: Antonio Quartulli <antonio@openvpn.net>