Don't rematch all requests when adding new ones

With the network selection rewrite in S, rematching a single request can
now easily be done; this can be used as an optimization in
handleRegisterNetworkRequests to avoid rematching all requests when
registering a new one.

This can be disabled by a flag that is unset by default,
REMATCH_ALL_REQUESTS_ON_REGISTER.

Test: atest ConnectivityServiceTest
Change-Id: If76f79b41ac88863974f7025624667134bea2570
4 files changed