[NAN] Replace int peerId with more opaqure Object peerHandle per API review

(cherry-pick of commit f02ae5e23cb59fcbd364907ecb1199424fc5eb62)

Bug: 31470256
Test: unit tests & integration (sl4a) tests.
Change-Id: I0225027b8e1a2d7cb5d27afc91b97ef9643f5dff
5 files changed