DataConnection: Use InetAddress.isNumeric rather than a regex.

android.util.Patterns is pretty heavy weight; it can take a long
time to initialize and can increase java heap usage (dirty memory)
by hundreds of kilobytes. InetAddress.isNumeric provides the same
functionality using getaddrinfo(..AI_NUMERIC) and friends, and
provides a guarantee that the resulting string will be parseable
by InetAddress.getByName and friends can parse it correctly.

Bug: 63107244
Test: DataConnectionTest

Change-Id: I9078aea83dd2da621576ff3328b975bd65c00b72