[udp] Move high-frequency debug messages to DBGLVL_EXTRA

This makes it possible to leave UDP debugging enabled in order to see
interesting UDP events, without flooding the console with at least one
message per packet.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[ipv6] Rename sin_{family,port} to sin6_{family,port} in struct sockaddr_in6

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[tcpip] Allow binding to unspecified privileged ports (below 1024)

Originally-implemented-by: Marin Hannache <git@mareo.fr>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
[nfs] Fix an issue with the selection of a local port

Reported-by: Robin Smidsrød <robin@smidsrod.no>
Signed-off-by: Marin Hannache <git@mareo.fr>
Signed-off-by: Michael Brown <mcb30@ipxe.org>