cam-service: Implement retry mechanism for accept()

Currently the code inside dispatch_thread is calling
accept() to establish the connections, however the accept()
function can sometimes fail with recoverable errors, but
the current code doesn't distinguish between recoverable and
catastrophic one and stops the cam-service.

To overcome this issue, implement a retry mechanism that
will retry the accept() call when it returns a recoverable
error, print also a debug message in that case before retrying.

Signed-off-by: Luca Fancellu <luca.fancellu@arm.com>