Let testable callbacks use Network directly

In retrospect it's surprising we didn't have this already but
the need didn't arise.

Bug: 139268426
Test: NetworkStackTests
Change-Id: If0616c60bac301c7d983d94474cd4264bf7df214
(cherry picked from commit 85a253dccab12e9c6b5b83ee5bec264a2c9ec173)
1 file changed