Move some code around.

Move some code around.

Move stuff to initialize and clean up libraries that are used by
netdissect code into nd_init() and nd_cleanup() routines in
libnetdissect; this includes Winsock (which is used on Windows by, for
example, the code to get names for IP addresses) and libsmi.

Call nd_init() when tcpdump starts up, and call nd_cleanup() when it
exits.

Move util.c routines to tcpdump.c, and make them static.

Use ndo->ndo_error to report a failure to open a file in print-esp.c.