selftests/bpf: Enable config options needed for xdp_synproxy test

This commit adds the kernel config options needed to run the recently
added xdp_synproxy test. Users without these options will hit errors
like this:

test_synproxy:FAIL:iptables -t raw -I PREROUTING -i tmp1 -p
tcp -m tcp --syn --dport 8080 -j CT --notrack unexpected error: 256
(errno 22)

Suggested-by: Alexei Starovoitov <[e-mail]>
Signed-off-by: Maxim Mikityanskiy <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/testing/selftests/bpf/config

···
 CONFIG_IKCONFIG=y
 CONFIG_IKCONFIG_PROC=y
 CONFIG_MPTCP=y
+CONFIG_NETFILTER_SYNPROXY=y
+CONFIG_NETFILTER_XT_TARGET_CT=y
+CONFIG_NETFILTER_XT_MATCH_STATE=y
+CONFIG_IP_NF_FILTER=y
+CONFIG_IP_NF_TARGET_SYNPROXY=y
+CONFIG_IP_NF_RAW=y