Disconnect via NetworkManager should send DHCPRELEASE when applicable

[Thomas Novin]

Hello

I think NetworkManager should send a DHCPRELEASE when the user chooses
disconnect on a DHCP-connection.

This is important when using a service that only allows one IP, then the
MAC/IP-combo is locked for whatever the DHCP lease-time is. Sending a
DHCPRELEASE frees up the lease making the service available for another
computer.

Any reason why not to do this? Should I file a Launchpad bug?

Rgds//Thomas