context: scale max_quantum and add quantum_limit

Also scale the max_quantum with the selected rate. Add a new
quantum_limit property that is the upper limit of the quantum regardless
of the sample rate, this is usually the allocated buffer size.

See #1931

src/daemon/client-rt.conf.in

@@ -9,6 +9,8 @@ context.properties = {
     #mem.allow-mlock = true
     #mem.mlock-all   = false
     log.level        = 0
+
+    #default.clock.quantum-limit = 8192
 }
 
 context.spa-libs = {