Moved #defines so that UIP_TCPIP_HLEN and UIP_LLH_LEN are defined before they are used
Make 0 the default link-layer header length, as far as uIP is concerned. Most currently used linke layers (specifically, 802.15.4) has adaptation layers that use separate buffers, so there is no need to reserve space in the uIP buffer.
Removed redundant #ifdef
Fixed a severe error in the bugfix: the conditional was reversed. The check must be if the TCP MSS is larger than the BUFSIZE and not the other way around.
Merge pull request #502 from adamdunkels/push/fix-the-ipv6-bugfix

Fix the IPv6 bugfix
Merge branch 'master' into qidevices

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>