libxt_TCPMSS: restore build with IPv6-less libcs
Commit v1.4.10-149-gea2a02f added an netinet/ip6.h include, which is
not available on systems without IPv6 header files.
Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
diff --git a/configure.ac b/configure.ac
index 5cb1b1b..6aa0b2a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -68,6 +68,7 @@
fi;
AC_SUBST([blacklist_modules])
+AC_CHECK_SIZEOF([struct ip6_hdr], [], [#include <netinet/ip6.h>])
AM_CONDITIONAL([ENABLE_STATIC], [test "$enable_static" = "yes"])
AM_CONDITIONAL([ENABLE_SHARED], [test "$enable_shared" = "yes"])