configure: fix wrong reference to the conntrack-tools

Reported-by: Jan Engelhardt <jengelh@inai.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/configure.ac b/configure.ac
index ac7c9c0..3012df4 100644
--- a/configure.ac
+++ b/configure.ac
@@ -154,8 +154,8 @@
 else
 	AC_MSG_WARN([flex version $flex_version found.
 	Version 2.5.33 or greater is required. You may experience problems
-	while compilating the conntrack-tools. Please, consider to upgrade
-	flex.])
+	while compilating the nftables compatibility layer for iptables.
+	Please, consider to upgrade flex.])
 fi
 
 regular_CFLAGS="-Wall -Waggregate-return -Wmissing-declarations \