Previously we simply turned on TCP Keep-Alive which relied on
per-distribution, per-operating system defaults for keep-alive options.
Here we set reasonable defaults since long running processes can get
stuck for hours on end by using system defaults. This also adds comments
around the options to explain why they're being set.
Closes-bug: 1477275
Related-bug: 1323862
Change-Id: Ibd53ae2d4d2455db0ebc9951e5c764befc57850f