Add classes for tcptuning. All the classes are taken from their
current versions on serenity (commit 11a627ce). All systems apart
from intserv use some subset of these classes, so include them in
this module to avoid unnecessary duplication.

Note: The tcptuning::bbr class currently is not used by any system
but the plan is for it to be soon (post-CentOS 7 upgrades) so include
that as well for future usage even though it looks like dead weight
right now.