ramips: Fix multicast ICMPv6 for the rt3050 ethernet switch.

The FCT2 esw register should be set to 0x2500C to have "unknown IPv6
multicast" packets broadcasted to every port, instead of dropped.
The previous value only let those packets go through ports 1 and 3.

"Unknown IPv6 multicast" packets include packets needed by ICMPv6 echo
requests addressed to well-known addresses, such as ff02::1 (MAC address
is 33:33:00:00:00:01 in this case).

Please note that by default ICMPv6 echo requests to ff02::1 are not replied
to by the router because of ip6tables considering those packets to be invalid.
But this is another bug/patch. ;)

Signed-off-by: Vittorio Gambaletta <openwrt@vittgam.net>

SVN-Revision: 49287