Instead of queuing all events for a subscriber, only queue more
important events if delivery of event notifications starts failing.
This allows more time for the subscriber to recover since the maximum
queue length if not reached because of Probe Request frames only.
Instead of dropping the subscription on first failure, allow up to
10 failures before dropping. In addition, drop the callback URLs
one by one instead of full subscription if only one URL is failing.
Instead of implementing HTTP client functionality inside
wps_upnp_event.c, use a generic HTTP client module to do this. The HTTP
client code can now be shared more easily for other purposes, too.
Allow more than one pending PutWLANMessage data to be stored (M2/M2D
from multiple external Registrars) and drop pending M2/M2D messages when
the Enrollee replies with M3.
This adds mostly feature complete external Registrar support with the
main missing part being proper support for multiple external Registrars
working at the same time and processing of concurrent registrations when
using an external Registrar.
This code is based on Sony/Saice implementation
(https://www.saice-wpsnfc.bz/) and the changes made by Ted Merrill
(Atheros) to make it more suitable for hostapd design and embedded
systems. Some of the UPnP code is based on Intel's libupnp. Copyrights
and licensing are explained in src/wps/wps_upnp.c in more detail.
