Fix: MAC OSX TotalLength of IP

At write the field must be in host byte order and at read the field is
in network byte order.

Signed-off-by: Gregory Detal <gregory.detal@uclouvain.be>
Add PacketFromIPv6 from RawLayer

Usefull when parsing ICMP content.

Signed-off-by: Gregory Detal <gregory.detal@uclouvain.be>