use cpu dependent stack size
use forwarding table entry when routing

So far the entry was looked up, but ignored in the case where the packet
has to be forwarded.
added missing hdr position shift
Merge pull request #867 from OlegHahm/uart_stacksize

uart: use cpu dependent stack size
Merge pull request #876 from OlegHahm/iphc_decompression_shift

net: 6lowpan: added missing hdr position shift
Merge pull request #875 from OlegHahm/ip_forwarding

net: IPv6: use forwarding table entry when routing