net: icmpv6: Removing dead code

Callback cannot be null so no need to check its value.

Coverity-CID: 157572

Change-Id: I26e4b24c41d30aa9007b78895975035e6bf8807f
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
1 file changed