regression: move_async/rtde_receive fails on UR5 since v1.5.0

This might be related to #67 (closed):

When I connect to our UR5 (running UR Software 3.11.0.82155) I can run all examples that rely solely on rtde_control. e.g. servoj works.

Whenever I run an example that contains rtde_receive I run into a synchronization issue:

$ ./move_async 
Unable to start synchronization
RTDE: socket timeout!
RTDEReceiveInterface Exception: Operation canceled

It then hangs and needs to be killed externally as it does not respond to signals at that point.

I confirmed the issue for v1.5.4, v1.5.3 as well as v1.5.2. I successfully built v1.5.1 and v1.5.0, after patching an issue regarding ostream and its missing iterator include, but running the programs did not work at all (I assume they were not uploaded properly, which is unrelated to this bug, but the reason why I did not confirm those two as well).

If there's a PR related to this issue, we can test it on the robot (this month at least).