configure: rename --disable-xtables to --disable-nftables

The compat utility name is xtables, the name used for the
compatibility binary. Better explicitly refer to the compatibility
later as nftables-compat.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/configure.ac b/configure.ac
index 3012df4..54f1fd5 100644
--- a/configure.ac
+++ b/configure.ac
@@ -61,7 +61,7 @@
 	[Path to the pkgconfig directory [[LIBDIR/pkgconfig]]]),
 	[pkgconfigdir="$withval"], [pkgconfigdir='${libdir}/pkgconfig'])
 AC_ARG_ENABLE([nftables],
-	AS_HELP_STRING([--disable-xtables], [Do not build xtables]),
+	AS_HELP_STRING([--disable-nftables], [Do not build nftables compat]),
 	[enable_nftables="$enableval"], [enable_nftables="yes"])
 
 libiptc_LDFLAGS2="";