Acct-Delay-Time missing with RADIUS accounting

[Nick Lowe]

Thinking more about the Interim-Update case, whether or not to resend
an Accounting-Request packet of this form should depend on when the
end of the next interval will fall.

If, for example, the end next interval is not going to be until 5
minutes away, hostapd absolutely should not wait until then to retry.

This, especially so with the newer code in hostapd that populates the
Framed-IP-Address attribute. Many people use this attribute for SSO
purposes, so there are strong real world justifications to get this
right.

(The Framed-IP-Address feature in itself should be improved as,
presently, an 'immediate' asynchronous Interim-Update isn't send as
the client's IP address becomes known or changes and hostapd will use
information that isn't sourced via DHCP snooping, which is unreliable
and easily spoofable.)

Cheers,

Nick