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.
Merge pull request #548 from pinwing/master

IPv6 Prefix Delegation fixes
webui: Shorten displayed FW version to buildno + extendno (i.e. 374.40_0)
webui: Display full FW version on Sysinfo page
netatalk: revert modified ssl path check
netatalk: set program-prefix to a blank value so --target is not used as a prefix
netatalk: Pass LD_LIBRARY_PATH to configure script
netatalk: Pass the path to libgcrypt-config to configure
netatalk: Adjust the BDB include path check for the build environment
netatalk: Modify library search path for Asuswrt build environment
netatalk: update gitignore
netatalk: Disable checking for dtrace

If dtrace was detected on the host it would be enabled, even
though it's not available on the target.
netatalk: Don't touch netatalk source dir before configuring
netatalk: Updated build files