Allow multiple tcp adb connection to same device.

This worked before Kitkat, and then we lost this feature in Kitkat.
Now I make the register logic in server_socket_thread as same as qemu_socket_thread.

Test: manual - build emulator image and connect from different adb client.
Bug: 32341562
Change-Id: I7b4831d280048d2a3796be3522bd3b8fbc1ade6b
Signed-off-by: Tao Wu <lepton@google.com>