ar71xx: Add support for the WNDR3800CH

Apparently this is a fairly common refurb unit of the 3800 series now,
with merely the recognition string changed in the boot loader.

Signed-off-by: Dave Taht <dave.taht@bufferbloat.net>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42023 3c298f89-4303-0410-b956-a3cf2f4a3e73
odhcpd: skip MSRs in RAs for prefixes with same size as DP

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42024 3c298f89-4303-0410-b956-a3cf2f4a3e73
odhcpd: correct incorrect commit-id in last commit

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42026 3c298f89-4303-0410-b956-a3cf2f4a3e73