In practice, this should only matter when there are multiple
header files with the same name. That is something we try
to avoid already, by giving headers a distinct name.

When building NetworkManager itself, we clearly want to use
double-quotes for including our own headers.
But we also want to do that in our public headers. For example:

  ./a.c
    #include <stdio.h>
    #include <nm-1.h>
    void main() {
        printf ("INCLUDED %s/nm-2.h\n", SYMB);
    }

  ./1/nm-1.h
    #include <nm-2.h>

  ./1/nm-2.h
    #define SYMB "1"

  ./2/nm-2.h
    #define SYMB "2"

$ cc -I./2 -I./1 ./a.c
$ ./a.out
INCLUDED 2/nm-2.h

Exceptions to this are
  - headers in "shared/nm-utils" that include <NetworkManager.h>. These
    headers are copied into projects and hence used like headers owned by
    those projects.
  - examples/C

Otherwise there is a warning:

  from gi.repository import GLib, NM
  __main__:1: PyGIWarning: NM was imported without specifying a version first. Use gi.require_version(NM, 1.0) before import to ensure that the right version gets loaded.

Add a timeout parameter and allow passing multiple interfaces to make
the script more useful for testing purposes.

Reported-by: Ali Nematollahi <alirezan1@gmail.com>