[krbdev.mit.edu #1210] KDC doesn't clean up after add_udp_fd()

[Tom Yu via RT]

in network.c, setup_udp_port() calls add_udp_fd() which calls add_fd().
 add_fd() in turn allocates a struct connection, which doesn't get freed
when the KDC shuts down.  This gets reported as a PLK or MLK by Purify.