nm_setting_user_set_data() rejects invalid keys and values, and
can fail. This API is correct never to fail, like the get_data()
only returns valid user-data.
However, the g_object_set() API allows to set the hash directly but
it cannot report errors for invalid values. This API is used to
initialize the value from D-Bus or keyfile, hence it is wrong
to emit g_critial() assertions for untrusted data.
It would also be wrong to silently drop all invalid date, because
then the user cannot get an error message to understand what happend.
The correct but cumbersome solution is to remember the invalid values
separately, so that verify() can report the setting as invalid.
(cherry picked from commit 1dbbf6fb03)
