#2 Socket exhaustion on Ubuntu/OS X

[nnp]

On Ubuntu an exception occurs after sending a few thousand INVITE requests against OpenSER with no CANCELs. This appears to be because the sockets used to send the INVITEs are never closed. This probably happens because OpenSER keeps trying to resend responses to the initial invite but we are not providing anything to handle these when do_cancel is false. As a result the transaction manager constantly updates the 'timeout' for the transaction and the socket is never cleaned up.

A quick fix is to set the transaction timeout from the fuzzer to 0 to begin with.