autoconf: change the message for failure to link with libpcap.
Such a failure *might* be the result of a bug, but it might also be the
result of building against a libpcap library with a different bit width
from the one being used for tcpdump, or attempting to do a static build
against a libpcap that doesn't support that (because it depends on other
libraries, one of which is only available as a dynamic library), etc..
The latter, rather than the former, appears to be the more common case
these days.
projects / tcpdump / commit
