Set the error message for "permission denied" errors.

Set the error message for "permission denied" errors.

Provide a suggestion for PCAP_ERROR_PERM_DENIED and
PCAP_ERROR_PROMISC_PERM_DENIED; the suggestion may be nothing more than
"you might require root permission", but at least it's something.

Note also what we were trying to do, to indicate that the problem might
be that you need root permission to set promiscuous mode even if you
don't need it to capture, or that you need CAP_NET_ADMIN permission to
change the time stamp mode of an adapter on Linux even though you don't
need it to capture.  (The latter was done as per the discussion in issue
and that triggered the same double-free bug that failing to set up the
memory-mapped ring buffer caused in issue #1054.)

(cherry picked from commit 92c547194ffa85c89b579658f1cc752fad98666f)