rtorrent: update to 0.9.6, disable ipv6

Update rtorrent to 0.9.6.
Update patches.
Disable ipv6 in rtorrent, as ipv6 is disabled also in libtorrent.

Libtorrent compilation has been broken since #1181 got merged
and ipv6 got enabled. Users have seen issues like #1316 and #1804

IPv6 support in libtorrent & rtorrent master is not complete.
Instead there is a separate ipv6 branch, which still needs some
cleanup before mainstream use. See discussion at
https://github.com/rakshasa/rtorrent/issues/59#issuecomment-56651538
So, it makes no sense to use ipv6 with the master branch.

Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>

net/rtorrent/patches/100-fix-cross_compile.patch

@@ -1,6 +1,6 @@
 --- a/configure.ac
 +++ b/configure.ac
-@@ -4,7 +4,6 @@ AC_DEFINE(API_VERSION, 8, api version)
+@@ -4,7 +4,6 @@ AC_DEFINE(API_VERSION, 9, api version)
  
  AM_INIT_AUTOMAKE
  AC_CONFIG_HEADERS(config.h)