Treat subscriber-irrelevant command responses as hotline messages
[stub]
there are only a few commands that are relevant to subscribers:
HELLO
GOODBYE
INVITE
espanol/frances/deautsch
all other commands are irrelevant from the subscriber perspective (in fact, most of the time we can safely assume they do not know they exist).
If they send in a message starting with any of those commands, the command responses should be thrown out and it should be treated as a hotline message.