libceph: print more info for short message header

If an osd client response message arrives that has a front section
that's too big for the buffer set aside to receive it, a warning
gets reported and a new buffer is allocated.

The warning says nothing about which connection had the problem.
Add the peer type and number to what gets reported, to be a bit more
informative.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>