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

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

Change-Id: I26a78dc6715a81c8f0d35c1f035e31685a41397c
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>