rfq: reduce min expiry to 10 seconds

This permits a wider range of RFQ quote expires, as a shorter quote
expiry serves to limit optionally.

Fixes: #1342

Author: Roasbeef

docs/rfq-and-decimal-display.md

@@ -369,6 +369,9 @@ use a price oracle, but its role is different for those parties:
   tasked with validating exchange rates offered to them by the edge node, to
   make sure they aren't proposing absurd rates (by accident or on purpose).
 
+**NOTE**: By default, the _minimum_ quote expiry at tapd node will accept is _10
+seconds_.
+
 Due to the fundamentally different roles of the price oracle for both parties,
 it is expected that the actual implementation for the price oracle is also
 different among the parties.

rfq/negotiator.go

@@ -17,7 +17,7 @@ import (
 const (
 	// minAssetRatesExpiryLifetime is the minimum asset rates expiry
 	// lifetime in seconds.
-	minAssetRatesExpiryLifetime = 60
+	minAssetRatesExpiryLifetime = 10
 
 	// DefaultAcceptPriceDeviationPpm is the default price deviation in
 	// parts per million that is accepted by the RFQ negotiator.