tests: stabilize test 2032 and 2033

Both these tests run the same underlying test code: libntlmconnect.c -
this test code made some assumptions about socket ordering when it used
curl_easy_fdset() and when we changed timing or got accidental changes
in libcurl the tests would fail.

The tests verify that the different transfers keep using the same
connections, which I now instead made sure by adding the number of bytes
each transfer gets and then verifies that they always get the same
amount as when these tests worked.

Closes #1576