Bug#610831: Notify user on link detection failure for static config

[Matthew Palmer <mpalmer@debian.org>]

Package: netcfg
Version: 1.59
Severity: wishlist
User: debian-qa@lists.debian.org
Usertags: gift

I've just committed a simple fix to static.c to allow netcfg to "pause"
until it finds a good link on a statically configured interface (look for
the netcfg_detect_link() call).

However, if link detection fails, the user isn't notified.  I've done this
because link detection isn't universal (ethtool-lite is known not to work on
wireless interfaces, for example), and I don't want to break things for
those users.  However, it is possible that the user selected the wrong interface
or the cable isn't plugged in, so it'd be nice if the user could be notified
about this.

Need to do the following:

* A new boolean template, like netcfg/static_link_detection_failed, that
  says something like "${interface} has been successfully configured, but no
  link has been detected.  This could be because your NIC doesn't support
  link detection, or you may have selected the wrong NIC or the cable is
  unplugged.  Would you like to continue using this NIC, or go back and
  choose another?"

* Detect whether netcfg_detect_link() succeeded or not.  If it didn't,
  present the user with the above template.

* If the user chooses "yes, continue", then all is well.  Otherwise, send
  the user back to the main netcfg menu to choose another interface.

It may be best to wait until #591012 is fixed, as .../carrier supports
wireless NICs.  Then there'll be far, *far* fewer false positives.

- Matt