vnic: add TODO list

• non-promisc mode
• multicast filter support

Also drop ARM64TODO comments; this is an issue with this specific
driver, not a general arm64 issue.

PR: 223575
PR: 223573

(cherry picked from commit 941650aae9762293f4c63788ddb17e0114828813)
(cherry picked from commit 29e9b487c1d427409a8bf1f893bc71a57c76f4b0)