libxtables12.symbols: add new symbol

New symbol added to the library in this last upstream release.
Signed-off-by: Arturo Borrero Gonzalez <arturo@debian.org>

debian/libxtables12.symbols

@@ -19,6 +19,7 @@ libxtables.so.12 libxtables12 #MINVER#
  xtables_find_match_revision@Base 1.8.0
  xtables_find_target@Base 1.6.0+snapshot20161117
  xtables_find_target_revision@Base 1.8.0
+ xtables_fini@Base 1.8.5
  xtables_free_opts@Base 1.6.0+snapshot20161117
  xtables_getethertypebyname@Base 1.8.1
  xtables_getethertypebynumber@Base 1.8.1