Allow payload len to be larger than 256 bytes
Allow the 6lowpan code to handle packets larger than 256 bytes
Added the const keyword to IP address arguments that are not (and should not be) changed by the callee
Added the const keyword to functions that use the tcpip_set_outputfunc(), which now takes a const argument
Merge pull request #431 from adamdunkels/push/ipv6-const

Make IP addresses const
Merge pull request #432 from adamdunkels/push/154-len

Allow the 802.15.4/6lowpan code to operate on packets larger than 256 bytes