SSH2: make it so negotiated algorithms can be seen before login

That's not really going to be do'able.

It works for `getEncryptionAlgorithmsClient2Server()` because the default value of `$this->encryption_algorithms_client_to_server` is `false`. So if `_connect()` fails the method returns false (the default value) and if it succeeds it returns the algorithms.

But in the case of `_login`...  if `_connect()` fails and it continues to run you'll get a bunch of notices / warnings / whatever. ie. "Not enough input", "connection closed prematurely" or some combination there-of.

ie. with `getEncryptionAlgorithmsClient2Server()` if `_connect()` return false you can continue running just fine. with `_login` if `_connect()` returns false you want to stop. Well, at least you do if `_connect()` hasn't previously been called.

`_login()` can be called multiple times. eg. multi-factor authentication. `_connect()` will only return true once. For each subsequent run it'll return false. So that's why the `$this->bitmap & NET_SSH2_MASK_CONSTRUCTOR` check is done.