Move PlainDatagramSocketImpl away from JNI (part 2)

Rewrites remaining JNI methods in PlainDatagramSocketImpl
(socket{Get,Set}Option) on top of IoBridge.

Adapted IoBridge behaviour to work with OpenJDK code. Since the only
other user of the affected method does not depend on the changed
behaviour, this won't introduce any side effect.

Test: CtsLibcoreTestCases
Bug: 28609551
Change-Id: I6310edd9ec3b48bb51a8cc86ecbe757d1096f5a1