Peers are identified by ids, which should be treated as opaque by service
libraries. Stack implementations should ensure that each PeerId identifies a
single peer over a single instance of the stack - a
[bt_gatt::Central::connect] should always attempt to connect to the
same peer as long as the PeerId was retrieved after the Central was
instantiated. PeerIds can be valid longer than that (often if the peer is
bonded)