Allow PUT on direction param in QoS minimum pps rule

Based on discussion in the previous review [1] and IRC [2], it was
decided to allow direction parameter in QoS minimum packet rate
rule to be updated with a PUT request. This behavior matches current
behavior of other QoS rules.

If the rule to be updated is associated with a bound port, the request
is going to be rejected by the server.

Since direction-oriented and direction-less QoS min pps rules are
mutually exclusive, the request is going to be rejected if it would
result in mixing direction-oriented and direction-less rules in a single
policy.

[1] https://review.opendev.org/802486
[2] https://meetings.opendev.org/irclogs/%23openstack-neutron/latest.log.html#t2021-08-09T07:56:39

Related-Bug: #1922237
See-Also: https://review.opendev.org/785236
Change-Id: If1f7b28184c740c30388f564b704ba42c8967527

api-ref/source/v2/parameters.yaml

@@ -4161,6 +4161,12 @@ min_kpps-response:
   in: body
   required: true
   type: integer
+min_kpps-update:
+  description: |
+    The minimum kilo (1000) packets per second (kpps) value.
+  in: body
+  required: false
+  type: integer
 min_prefixlen:
   description: |
     The smallest prefix that can be allocated from a
@@ -4948,6 +4954,16 @@ qos-rule-minimum-packet-rate-direction:
   in: body
   required: true
   type: string
+qos-rule-minimum-packet-rate-direction-update:
+  description: |
+    The direction of the traffic to which the QoS
+    minimum packet rate rule is applied, as seen
+    from the point of view of the ``port``. Valid
+    values are ``any``, ``egress`` and
+    ``ingress``.
+  in: body
+  required: false
+  type: string
 qos-rule-type:
   description: |
     The type of QoS rule.

api-ref/source/v2/qos.inc

@@ -1131,7 +1131,7 @@ code 501, if there is any bound port referring to the rule via the qos policy.
 
 Normal response codes: 202
 
-Error response codes: 400, 401, 404, 501
+Error response codes: 400, 401, 404, 409, 501
 
 Request
 -------
@@ -1141,7 +1141,8 @@ Request
    - policy_id: qos-policy-id-path
    - rule_id: qos-rule_id
    - minimum_packet_rate_rule: minimum_packet_rate_rule
-   - min_kpps: min_kpps
+   - min_kpps: min_kpps-update
+   - direction: qos-rule-minimum-packet-rate-direction-update
 
 Request Example
 ---------------

api-ref/source/v2/samples/qos/minimum_packet_rate_rule-update-request.json

@@ -1,5 +1,6 @@
 {
     "minimum_packet_rate_rule": {
-        "min_kpps": 2000
+        "min_kpps": 2000,
+        "direction": "any"
     }
 }

neutron_lib/api/definitions/qos_pps_minimum_rule.py

@@ -46,7 +46,7 @@ SUB_RESOURCE_ATTRIBUTE_MAP = {
             },
             qos_constants.DIRECTION: {
                 'allow_post': True,
-                'allow_put': False,
+                'allow_put': True,
                 'is_visible': True,
                 'default': None,
                 'is_filter': True,