Move-assign a basic_stream_socket
from another.
basic_stream_socket & operator=( basic_stream_socket && other);
This assignment operator moves a stream socket from one object to another.
The other basic_stream_socket
object
from which the move will occur.
Following the move, the moved-from object is in the same state as if
constructed using the basic_stream_socket(const executor_type&)
constructor.