Summary:
Add support for Mux protocol.

From GH: https://github.com/pixie-io/pixie/pull/327



Closes #327

Test Plan: Frame parsing tests included.

Reviewers: #stirling, rcheng

Reviewed By: #stirling, rcheng

Subscribers: rcheng, yzhao
Signed-off-by: Dom Del Nano <ddelnano@gmail.com>

Differential Revision: https://phab.corp.pixielabs.ai/D10030

GitOrigin-RevId: f0206a1d62b2455c4e2afe7a3fd0dd40d3e7fde8