netfilter: xtables: add missing header files to export list

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
diff --git a/include/linux/netfilter/Kbuild b/include/linux/netfilter/Kbuild
index 9f11fbc..fc4e0aa 100644
--- a/include/linux/netfilter/Kbuild
+++ b/include/linux/netfilter/Kbuild
@@ -56,6 +56,8 @@
 header-y += xt_realm.h
 header-y += xt_recent.h
 header-y += xt_sctp.h
+header-y += xt_secmark.h
+header-y += xt_socket.h
 header-y += xt_state.h
 header-y += xt_statistic.h
 header-y += xt_string.h