net: icmpv6: Do not set destination ll address

We must not set destination link layer address when generating
ICMPv6 Echo-Reply message. The reason is that the address must
come from neighbor cache right before the reply is sent to the
network.

Jira: ZEP-1360

Change-Id: I32a23f5689107b6827728cce67a5d27fa964ebd2
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>