net: Use proper ll header length when sending IPv6 NS

We must use the link layer header length derived from the
actual interface when sending IPv6 neighbor solicitation msg.

Change-Id: I1836743ffed50254c89341fbdade039741e62f33
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
1 file changed