How can I make Time Machine work with my Netgear WNDR3700 router?
Look at http://netatalk-ddwrt.blogspot.com/ 

Try the builds mentioned and install them on your router with the following commands:

ipkg install libdb_4.7.25-3_mipsel.ipk
ipkg install netatalk_2.2.0-2_mipsel.ipk

make sure that you use

ipkg install libdb_4.7.25-3_mipsel.ipk -force-downgrade

in case your libdb version is newer than 4.7.24.

Best regards,
 nGoot