Changed default send slow start threshold to MaxInt32 to allow compil…

[oxtoacart]

…ing on 32 bit platforms

I'm trying to use netstack on an Android phone and need to be able to compile on 32 bit. This addresses that.

[iangudger]

We don't accept pull requests on this repository. Please see CONTRIBUTING.md for how to send us a patch.

As for the actual patch itself, it should be possible to make it only apply to 32bit systems with build constraints.

[googlebot]

We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for all the commit author(s) or Co-authors. If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.
In order to pass this check, please resolve this problem and have the pull request author add another comment and the bot will run again. If the bot doesn't comment, it means it doesn't think anything has changed.

ℹ️ Googlers: Go here for more info.