Added check to prevent applications from connecting to self

[ethouris]

There's a problem when the Rendezvous connection mistakenly specifies a self address. In this case the connection facility gets confused by getting back packets that the agent himself has sent, taking these sent packets as if they came from the peer. This leads to misleading errors that result from interpreting packets that the agent shouldn't have received in the first place.

This fix causes error when srt_connect is called with target address that:

• matches the adapter address, if the adapter IP was configured
• matches any of the local machine IP addresses, if the socket was bound to INADDR_ANY

[rndi]

Won't this add iphlpapi.dll as dependency for all apps, not just "testing" which the only place where it is currently needed?

[ethouris]

This check is predicted to be done by all applications that make SRT connections, so this would be simply a complicated conditional slalom, to be withdrawn later anyway.

[rndi]

No need for complicated slalom, just add a quick and dirty block, maybe a parameter to 'srt_make_application', that will be easy to remove later if and when we decide to add iphlpapi.dll dependancy to all apps.

[ethouris]

This will be added to EVERY application, as long as explicitly requested. For Linux & Mac it will be always done (needs no extra features from the system). For Windows, it requires extra ENABLE_CONSELF_CHECK_WIN32 flag as it implies linking against extra Iphlpapi.lib.

[ethouris]

Current status: The current solution on Windows uses iphlpapi library which is deemed unreliable. For Windows there must be found some alternative method to list the IP addresses assigned to local NICs. Possible further steps:

• Keep this PR in OnHold state until the solution for Windows is found
• Remove the implementation on Windows here and make a new PR to provide the solution for this on Windows.

[ethouris]

Current status: A new flag has been added, which allows this prevention to be done in the applications also on Windows, as it requires an extra Iphlpapi.lib dependency. On Linux and BSD this is always done.