IPv6 Prefix Delegation fixes

After receiving an IPv6 prefix via DHCPv6-PD, the prefix is not
advertised until dhcp6c-state is manually called in the router.

If DHCPv6-PD is enabled and no DNS is acquired from the router
advertisement, try to retrieve the DNS via the DHCPv6 client.
Don't advertise IPv6 MTU for native interfaces

IPv6 tunnel interfaces have a 20 byte overhead (IPv4 header size).
Native IPv6 does not have this limitation.
Remove case IPV6_NATIVE_DHCP: before default:

As suggested in the pull request, removing the explicit IPV6_NATIVE_DHCP case and letting the default case handle it.
Always request DNS servers via dhcp6c

As proposed in the pull request, always request DNS servers without looking at ipv6_ra_conf for now.
Updated SDK5/RT-N16 binary blobs with GPL 4422 files
Removed unused file
Remove these modules as they should be generated by the built process
Updated gitignore
We now have up-to-date emf binary blobs, so remove our temporary forced prebuilt module copy for MIPS devices
Updated MIPS emf build environment to be in-sync with ARM (and Asus 4561)
Merged with GPL 374.4561 (AC68)
Merged MIPS versions of the emf binary blobs from 4422_n16 GPL
dropbear: Updated to 2014.63
Don't spoil it if you understand what this does ;)
ufsd: Fixed build environment for ARM
This looks better
Merge pull request #548 from pinwing/master

IPv6 Prefix Delegation fixes
wl: Reverted RT-AC68U driver to 374_583 (attempting to fix random reboots)
webui: Shorten displayed FW version to buildno + extendno (i.e. 374.40_0)
webui: Display full FW version on Sysinfo page