This patch simplify the handling to set fields inside of struct ipv6hdr
to zero. Instead of setting some memory regions with memset to zero we
initialize the whole ipv6hdr to zero.

This is a simplification for parsing the 6lowpan header for the upcomming
patches.
Signed-off-by: NAlexander Aring <alex.aring@gmail.com>
Reviewed-by: NWerner Almesberger <werner@almesberger.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>