Remove orphaned wpa_cli control socket on EADDRINUSE

Remove orphaned wpa_cli control socket on EADDRINUSE

If the bind() on /tmp/wpa_ctrl_<pid>_<in-proc-counter> fails with
EADDRINUSE, there is an existing socket file with the name we are trying
to create. Since getpid() is unique, there cannot be another process
using that socket and we can just unlink the file and try again. This
can speed up client connection if wpa_cli is killed without allowing it
to clean up the socket file. [Bug 288]