Building NetworkAgentConfig in shim instead of in test

NetworkAgentConfig.Builder is not available in Q device since
the methods are not in the API surface. The connectivity code is
not modularized, either. Tests should not use it directly.

Replace the usage with shim instead.

Bug: 227694406
Test: atest NetworkStackTests:NetworkMonitorTest in T and Q device
Change-Id: I96106d5ff15e847dab2accad97bc2ea442019421
3 files changed