[core] Fix for srt_connect() in the blocking mode

[maxsharabayko]

Under certain conditions m_bConnecting variable on a socket might not be reset to false after a connection attempt has failed.
In that case any further call to srt_connect will return SRT_ECONNSOCK:
"Operation not supported: Cannot do this operation on a CONNECTED socket"

In general case the receiver's worker thread sets m_bConnecting to false on timeout. That thread checks for a timeout roughly every 10 ms.

There is another check for TTL in the srt_connect function itself:

if (CTimer::getTime() > ttl)
{
	// timeout
	e = CUDTException(MJ_SETUP, MN_TIMEOUT, 0);
	break;
}

That check happens every second (or on a spurious wake up on a conditional variable m_PassCond in CRcvQueue::recvfrom()).

In case it was srt_connect thread, that handles the connection timeout, it does not reset the m_bConnecting variable to false. In that case any further call to srt_connect will fail to connect.

A regression unit test is added, although it is a matter of probability whether it catches the issue.

[ethouris]

I'd suggest making the 5555 port surely not bound with an SRT listener and surely not used by any other service. Otherwise the test may be thwarted by a service occupying port 5555.

To achieve that, you may start with 5000 and probably go up with the number while trying to bind a UDP socket to this port. Once successful, you can use this port in the test, then release it. For UDP it doesn't matter if anyone is reading from the port into which packets are otherwise coming.

[maxsharabayko]

@ethouris Added UDP port check before connection timeout tests.

[ethouris]

All ok, consider preserving the port before test.