extensions: libxt_NETMAP: rename IPv4 manpage and tell about IPv6 support

This patch renames libipt_NETMAP.man to libxt_NETMAP.man thus informing
about the IPv6 version.

Signed-off-by: Mart Frauenlob <mart.frauenlob@chello.at>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/extensions/libipt_NETMAP.man b/extensions/libxt_NETMAP.man
similarity index 88%
rename from extensions/libipt_NETMAP.man
rename to extensions/libxt_NETMAP.man
index a7e90b8..06507db 100644
--- a/extensions/libipt_NETMAP.man
+++ b/extensions/libxt_NETMAP.man
@@ -7,3 +7,5 @@
 Network address to map to.  The resulting address will be constructed in the
 following way: All 'one' bits in the mask are filled in from the new `address'.
 All bits that are zero in the mask are filled in from the original address.
+.TP
+IPv6 support available since Linux kernels >= 3.7.