mesh11sd: add new package

mesh11sd: add new package

Mesh11sd autonomously manages all aspects of an 802.11s mesh
network, with dynamic mesh parameters across all nodes and point to
multi-point vxlan tunneling.

Moved from the openwrt/routing feed, as discussed in
https://github.com/openwrt/routing/issues/184.

Carries three backports on top of the routing feed's copy, all from
the 7.2.0 development cycle and all pointed out by upstream:

- 443cdb4c handles the informational options before get_current_setup()
  runs. The setup pass waits for br-lan through wait_for_interface(),
  so on a host without that bridge "mesh11sd -v" took the full
  interface_timeout, ten seconds by default. That is invisible on a
  running router and fatal in the package CI, which kills each version
  probe after ten seconds.
- 9d18091f makes the script header agree with the LICENSE file the
  project ships. It claimed GPL version 3 or later while the file is
  GPL version 2, so PKG_LICENSE follows it to GPL-2.0-or-later.
- d0db5353 fixes a typo in get_current_setup(): the length came from
  $apmon_cgi_dir, which is never set, so strlen was always 0 and the
  trailing slash check read the wrong character.

The submenu is Mesh rather than the Network top level the feed copy
used; the other mesh packages follow once the move from the routing
feed is complete.

Signed-off-by: Josef Schlehofer <redacted>