selftests: net: give more time for GRO aggregation

The gro.sh test-case relay on the gro_flush_timeout to ensure
that all the segments belonging to any given batch are properly
aggregated.

The other end, the sender is a user-space program transmitting
each packet with a separate write syscall. A busy host and/or
stracing the sender program can make the relevant segments reach
the GRO engine after the flush timeout triggers.

Give the GRO flush timeout more slack, to avoid sporadic self-tests
failures.

Fixes: 9af771d2ec04 ("selftests/net: allow GRO coalesce test on veth")
Signed-off-by: Paolo Abeni <[e-mail]>
Reviewed-by: Eric Dumazet <[e-mail]>
Tested-by: Eric Dumazet <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

tools/testing/selftests/net/setup_veth.sh

···
 	local -r ns_mac="$4"
 
 	[[ -e /var/run/netns/"${ns_name}" ]] || ip netns add "${ns_name}"
-	echo 100000 > "/sys/class/net/${ns_dev}/gro_flush_timeout"
+	echo 1000000 > "/sys/class/net/${ns_dev}/gro_flush_timeout"
 	ip link set dev "${ns_dev}" netns "${ns_name}" mtu 65535
 	ip -netns "${ns_name}" link set dev "${ns_dev}" up