We were setting GLIB_VERSION_MAX_ALLOWED to 2.34, since we provide
reimplementations of a few 2.34 functions in nm-glib-compat.h. But
this was turning off warnings for the 2.34+ APIs we *didn't* have
compat versions of too.

Fix this by setting MAX_ALLOWED to 2.32 (same as MIN_REQUIRED), and
defining macros to wrap calls to compat-ified functions and disable
deprecation warnings around them.

This points out several places where we were accidentally using 2.34
APIs without noticing, which need to be fixed now.