flags: make -http and -https default to the public network address
flags: make -http and -https default to the public network address

In general, when people run Upspin servers they want them to be
accessible from the outside world. Listening on ":443" is more useful
than the previous default of "localhost:443". In partcular, this means
you can often run upspinserver without any command-line arguments.

Change-Id: I285a20bae3822d8148689ea2617775094a26f87a
Reviewed-on: https://upspin-review.googlesource.com/7868
Reviewed-by: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@google.com>
Reviewed-by: David Presotto <516b9783fca517eecbd1d064da2d165310b19759@google.com>
Reviewed-by: Eduardo Pinheiro <55040cbb39ba395339ae7940d8da6cd97797a4a8@google.com>

upspin/upspin,upspin/upspin