Bug 992922: Move connect operation to |DroidSocketImpl|, r=echou, f=shuang

With this patch, the connect operation for Bluedroid sockets
runs on the I/O thread. The related interface is identical to
the one of |UnixSocketConsumer|.
Bug 992922: Move listen operation to |DroidSocketImpl|, r=echou, f=shuang

With this patch, the listen operation for Bluedroid sockets
runs on the I/O thread. The related interface is identical to
the one of |UnixSocketConsumer|.
Bug 992922: Cleanup unused code for Bluedroid sockets