selftests: net: add missing config for big tcp tests

The big_tcp test-case requires a few kernel knobs currently
not specified in the net selftests config, causing the
following failure:

  # selftests: net: big_tcp.sh
  # Error: Failed to load TC action module.
  # We have an error talking to the kernel
...
  # Testing for BIG TCP:
  # CLI GSO | GW GRO | GW GSO | SER GRO
  # ./big_tcp.sh: line 107: test: !=: unary operator expected
...
  # on        on       on       on      : [FAIL_on_link1]

Add the missing configs

Fixes: 6bb382bc ("selftests: add a selftest for big tcp")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Acked-by: Aaron Conole <aconole@redhat.com>
Acked-by: Xin Long <lucien.xin@gmail.com>
Link: https://lore.kernel.org/all/21630ecea872fea13f071342ac64ef52a991a9b5.1706282943.git.pabeni@redhat.com/Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/config

@@ -29,7 +29,9 @@ CONFIG_NF_NAT=m
 CONFIG_IP6_NF_IPTABLES=m
 CONFIG_IP_NF_IPTABLES=m
 CONFIG_IP6_NF_NAT=m
+CONFIG_IP6_NF_RAW=m
 CONFIG_IP_NF_NAT=m
+CONFIG_IP_NF_RAW=m
 CONFIG_IPV6_GRE=m
 CONFIG_IPV6_SEG6_LWTUNNEL=y
 CONFIG_L2TP_ETH=m
@@ -45,6 +47,8 @@ CONFIG_NF_TABLES=m
 CONFIG_NF_TABLES_IPV6=y
 CONFIG_NF_TABLES_IPV4=y
 CONFIG_NFT_NAT=m
+CONFIG_NETFILTER_XT_MATCH_LENGTH=m
+CONFIG_NET_ACT_CT=m
 CONFIG_NET_ACT_GACT=m
 CONFIG_NET_CLS_BASIC=m
 CONFIG_NET_CLS_U32=m
@@ -55,6 +59,7 @@ CONFIG_NET_SCH_HTB=m
 CONFIG_NET_SCH_FQ=m
 CONFIG_NET_SCH_ETF=m
 CONFIG_NET_SCH_NETEM=y
+CONFIG_NF_FLOW_TABLE=m
 CONFIG_PSAMPLE=m
 CONFIG_TCP_MD5SIG=y
 CONFIG_TEST_BLACKHOLE_DEV=m