...when "nmcli" is called without argument and the master device is the last
entry printed.

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

The ifcfg-rh plugin may want to update its MASTER= key accordingly for
better compatibility with the legacy network service.

This will make it possible for the pages to commit slave connections
when the master connection is saved.

This is useful when master connections are saved potentially influencing
how slave connections are serialized.

This makes it more likely that the user will end up with a master
connection that has connection.interface-name property. This makes it
possible for ifcfg plugin to specify the master in the for of device
name (as opposed to UUID) for compatibility with the legacy network
tooling.

This is equivalent to what nmcli does.

https://bugzilla.redhat.com/show_bug.cgi?id=1369091