DcController: Compare LinkAddress Subset

Only the Address, Prefix Length, and Scope should be used when
comparing LinkAddresses. The Flags, Deprecation Time, and
Expiration Time can update at any time for a specific
LinkAddress.

Test: Manual
Bug: 184838873
Merged-In: Ide7bf63279b0db6a261735d82b39ae7a263ccdb4
Change-Id: Ide7bf63279b0db6a261735d82b39ae7a263ccdb4
(cherry picked from commit 5b7e8abe)