Timestamp VPN packets at all important points during transmission

[kamirr]

This will allow for pinpointing bottlenecks hindering the transmission rate.

Timestamps will be necessary, at the very least, around the following subsystems:

• GSB
• VPN
• VM

Possible issues:

• Collecting this debug data should not impact performance considerably.
• Should be possible to disable.

Open questions:

• Actually attach data to packets, or print to logs and then combine them from partaking machines?
  • IMO the second one: simpler and lower overhead