wireguard: selftests: load nf_conntrack if not present

Some distros may not load nf_conntrack by default, which will cause
subsequent nf_conntrack sets to fail. Load this module if it is not
already loaded.

Fixes: e7096c1 ("net: WireGuard secure network tunnel")
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
[ Jason: add [[ -e ... ]] check so this works in the qemu harness. ]
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Link: https://patch.msgid.link/20241117212030.629159-4-Jason@zx2c4.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: liuhangbin

tools/testing/selftests/wireguard/netns.sh

@@ -332,6 +332,7 @@ waitiface $netns1 vethc
 waitiface $netns2 veths
 
 n0 bash -c 'printf 1 > /proc/sys/net/ipv4/ip_forward'
+[[ -e /proc/sys/net/netfilter/nf_conntrack_udp_timeout ]] || modprobe nf_conntrack
 n0 bash -c 'printf 2 > /proc/sys/net/netfilter/nf_conntrack_udp_timeout'
 n0 bash -c 'printf 2 > /proc/sys/net/netfilter/nf_conntrack_udp_timeout_stream'
 n0 iptables -t nat -A POSTROUTING -s 192.168.1.0/24 -d 10.0.0.0/24 -j SNAT --to 10.0.0.1