The compare pattern seems simple, but seems error prone and subtle.
NM_CMP*() avoids that.
For example, nm_access_point_get_strength() returns an uint8_t.
C will promote those values to "int" before doing the subtraction.
Likewise, nm_access_point_get_frequency() returns a uint32_t. This
gets promoted to unsigned int when doing the subtraction. Afterwards,
that is converted to a signed int.
So both cases were in fact correct. But such things are not obvious.
Also, as fallback sort by D-Bus path. While that is not semantically
useful, we should use a defined sort order.