Set socket reuseaddr to true while checking free port

[xoriole]

Fixes #7847

[drew2a]

Nice improvement. Could you educate me a bit and share how this change fixes the issue?

[xoriole]

If the local application dies while a connection is active, the port will be tied up in TIME_WAIT. This is also true if the application dies while a connection is pending.
TIME_WAIT is the state that typically ties up the port for several minutes after the process has completed.

@drew2a Here is a nice write-up about Bind: Address Already in Use issue
https://hea-www.harvard.edu/~fine/Tech/addrinuse.html

[drew2a]

Thank you for the article!

I now understand that you modified NetworkUtils.is_port_free() to allow it to return TRUE for ports that are in the TIME_WAIT status.

[drew2a]

Allowing NetworkUtils.is_port_free() to return TRUE for ports that are in the TIME_WAIT status leads to two consequences:

1. It allows the GUI to reuse a port that is in TIME_WAIT status (which solves the issue with the Application Tester).

tribler/src/tribler/gui/tribler_window.py

Lines 166 to 170 in becc727

	if not default_network_utils.is_port_free(api_port):
	raise RuntimeError(
	"Tribler configuration conflicts with the current OS state: "
	"REST API port %i already in use" % api_port
	)

2. It allows NetworkUtils.get_random_free_port() and NetworkUtils.get_first_free_port() to use ports in TIME_WAIT status.

Both cases are risky as there could be a third-party application (not Tribler) that is leaving the port in TIME_WAIT to restore it later.

Although this fix resolves the issue with the Application Tester, it could lead to more severe problems in production.

I suggest solving the problem by using a random port for each consecutive Application Tester run (currently, it uses 20100 all the time).

[xoriole]

I have implemented another PR #7859 as an alternative solution to the current PR.
Closing this PR in favor of #7859.