[PATCH] generic: Remove IPv6 depependency of bridge in 2.6.38+

[PATCH] generic: Remove IPv6 depependency of bridge in 2.6.38+
Since 2.6.38 the bridge module has a dependency to IPv6 if IPv6 is
enabled. Since the IPv6 module isn't exactly lightweight and bridge also
only needs a single function from IPv6, it's rather easy to create a
common "lib" module with a RCU pointer to the actual implementation, if
the IPv6 module is loaded (although slightly hackish).

The codepath seems to be only taken when using IPv6, so there should be
no negative side effects when IPv6 isn't loaded. I did not measure how
big the performance impact is.

Signed-off-by: Jonas Gorski <jonas.gorski+openwrt@gmail.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@27237 3c298f89-4303-0410-b956-a3cf2f4a3e73