Extract RingBuffer class from NetdEventListenerService

This patch takes out the ring buffer array added for NFLOG wakeup packet
events logging and extract it into its own class for reuse. This new
RingBuffer class has the two minimal useful functions append() and
toArray().

Bug: 65164242
Bug: 65700460
Test: runtest frameworks-net, with new unit test
Change-Id: Ib94d79a93f4e99661b7d0fac67117b91d57af980