build: bump SONAME for libxtables

Commit v1.4.17-16-gefcdba4 updated structs in xtables.h, so age must
become 0 and vcurrent be increased. The latter has already happened in
v1.4.17-6-gd1e7922.

Signed-off-by: Jan Engelhardt <jengelh@inai.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/configure.ac b/configure.ac
index ffd088c..27e0b10 100644
--- a/configure.ac
+++ b/configure.ac
@@ -3,7 +3,7 @@
 
 # See libtool.info "Libtool's versioning system"
 libxtables_vcurrent=10
-libxtables_vage=1
+libxtables_vage=0
 
 AC_CONFIG_AUX_DIR([build-aux])
 AC_CONFIG_HEADERS([config.h])