selftests/net: Add xt_policy config for xfrm_policy test

When running Kselftests with the current selftests/net/config
the following problem can be seen with the net:xfrm_policy.sh
selftest:

# selftests: net: xfrm_policy.sh
[ 41.076721] IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
[ 41.094787] IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
[ 41.107635] IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
# modprobe: FATAL: Module ip_tables not found in directory /lib/modules/6.1.36
# iptables v1.8.7 (legacy): can't initialize iptables table `filter': Table does not exist (do you need to insmod?)
# Perhaps iptables or your kernel needs to be upgraded.
# modprobe: FATAL: Module ip_tables not found in directory /lib/modules/6.1.36
# iptables v1.8.7 (legacy): can't initialize iptables table `filter': Table does not exist (do you need to insmod?)
# Perhaps iptables or your kernel needs to be upgraded.
# SKIP: Could not insert iptables rule
ok 1 selftests: net: xfrm_policy.sh # SKIP

This is because IPsec "policy" match support is not available
to the kernel.

This patch adds CONFIG_NETFILTER_XT_MATCH_POLICY as a module
to the selftests/net/config file, so that `make
kselftest-merge` can take this into consideration.

Signed-off-by: Daniel Díaz <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

tools/testing/selftests/net/config

···
 CONFIG_AMT=m
 CONFIG_VXLAN=m
 CONFIG_IP_SCTP=m
+CONFIG_NETFILTER_XT_MATCH_POLICY=m