Bug 15006: [QA Follow-up] Only handle login requests in raw_transport

Bug 15006: [QA Follow-up] Only handle login requests in raw_transport

Although mainly hypothetical, it would still be possible to get
response from the server for an acs resend request. (This exception
is allowed in MsgType::handle.)
I also noticed that the response may well be a message from an older
session still.
This patch just removes that exception by only passing login requests
to sub handle in the raw_transport loop.

Test plan:
[1] Verify normal login procedure for raw.
[2] Check a few acs resend requests in raw. They should terminate without
    a response.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>