At some point we'll be passing other info like whether we need
the 802.1x identity too, or unknown CA certificate data for the
Agent to accept, etc. Basically state that instead of only
hints from the setting, we can pass other stuff as well.
If we can authenticate the agent for 'modify' permission, then send
any existing system secrets to it as the user has permission to change
those secrets. This means the agent doesn't have to call GetSecrets()
itself, which means simpler code on the agent side for a slight LoC
hit in NM itself.
This also moves the permissions checking into the NMAgentManager to
check each agent, which is sub-optimal since now the agent manager
has to do PolicyKit stuff, but hey that's life. Agents need secrets,
and we do need to authenticate every agent before we send secrets to
them, and the NMSettingsConnection doesn't know about individual
agents at all.
Allows NM to signal to an agent that an in-progress secrets
request is no longer needed. This could happen if the device
for which the request was started was removed, disabled, or the
network being connected to changed, or whatever.
