[Tunnelbroker][lib] cleanup Device <-> Tunnelbroker message types

Summary:
ENG-8621.

This improves readability, we can distingiush direction of message sender and recipient.

Test Plan: This only changes types, should not affect logic or content of messages sent between device <-> Tunnelbroker so only yarn flow:all and cargo check.

Reviewers: bartek, tomek

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D12856