Add ICMPv6 NS Souce Link Layer Option Length constant am: 9c87172ad2 am: b9107581df

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/3113219

Change-Id: I975992b12e32c180d266d3284fd7e977128e795f
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>