RootCanal: Refactor legacy LE advertising commands

Implement HCI parameter validation as required by the
specification. Resolve or generate private addresses
when required in 6.B.6.2 Privacy in advertising mode.

Test: gd cert
Test: atest --host --no-bazel rootcanal_hci_test
Change-Id: I83d2bbad31ec41c4c8b5c27c6280530bfb8dbb6a