dpp: set cap on the PKEX timeout, and reduce once PKEX finishes

If we scan a huge number of frequencies the PKEX timeout can get
rather large. This was overlooked in a prior patch who's intent
was to reduce the PKEX time, but in these cases it increased it.
Now the timeout will be capped at 2 minutes, but will still be
as low as 10 seconds for a single frequency.

In addition there was no timer reset once PKEX was completed.
This could cause excessive waits if, for example, the peer left
the channel mid-authentication. IWD would just wait until the
long PKEX timeout to eventually reset DPP. Once PKEX completes
we can assume that this peer will complete authentication quickly
and if not, we can fail.

src/dpp.c

@@ -2831,6 +2831,12 @@ static bool dpp_pkex_start_authentication(struct dpp_sm *dpp)
 
 	dpp_property_changed_notify(dpp);
 
+	/*
+	 * No longer waiting for an arbitrary peer to respond, reduce the
+	 * timeout now that we are proceeding to authentication
+	 */
+	dpp_reset_protocol_timer(dpp, DPP_AUTH_PROTO_TIMEOUT);
+
 	if (dpp->role == DPP_CAPABILITY_ENROLLEE) {
 		dpp->new_freq = dpp->current_freq;
 
@@ -4283,10 +4289,11 @@ static uint32_t *dpp_default_freqs(struct dpp_sm *dpp, size_t *out_len)
 
 static void __dpp_pkex_start_enrollee(struct dpp_sm *dpp)
 {
+	uint32_t timeout = minsize(DPP_PKEX_PROTO_TIMEOUT,
+			dpp->freqs_len * DPP_PKEX_PROTO_PER_FREQ_TIMEOUT);
 	dpp->current_freq = dpp->freqs[0];
 
-	dpp_reset_protocol_timer(dpp,
+	dpp_reset_protocol_timer(dpp, timeout);
-			dpp->freqs_len * DPP_PKEX_PROTO_PER_FREQ_TIMEOUT);
 
 	l_debug("PKEX start enrollee (id=%s)", dpp->pkex_id ?: "unset");