Add Ping4 offload for APFv6 multi-devices tests

Introduce Ping4 offload support for improved APFv6 multi-device testing.
Adds a decorator to restrict tests to Android B+ capable client device.

Test: m connectivity_multi_devices_snippet && atest CtsConnectivityMultiDevicesTestCases
Change-Id: I01909c1725ba471726223deef325c3f0a80b5c14
2 files changed