lib/tc: add ingress ratelimiting support for tc-offload

Firstly this patch introduces the notion of reserved priority, as the
filter implementing ingress policing would require the highest priority.
Secondly it allows setting rate limiters while tc-offloads has been
enabled. Lastly it installs a matchall filter that matches all traffic
and then applies a police action, when configuring an ingress rate
limiter.

An example of what to expect:

OvS CLI:
ovs-vsctl set interface <netdev_name> ingress_policing_rate=5000
ovs-vsctl set interface <netdev_name> ingress_policing_burst=100

Resulting TC filter:
filter protocol ip pref 1 matchall chain 0
filter protocol ip pref 1 matchall chain 0 handle 0x1
  not_in_hw
	action order 1:  police 0x1 rate 5Mbit burst 125Kb mtu 64Kb
action drop/continue overhead 0b
        ref 1 bind 1 installed 3 sec used 3 sec
        Action statistics:
        Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
        backlog 0b 0p requeues 0

MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to
10.0.0.200 () port 0 AF_INET : demo
Recv   Send    Send
Socket Socket  Message  Elapsed
Size   Size    Size     Time     Throughput
bytes  bytes   bytes    secs.    10^6bits/sec

131072  16384  16384    60.13       4.49

ovs-vsctl list interface <netdev_name>
_uuid               : 2ca774e8-8b95-430f-a2c2-f8f742613ab1
admin_state         : up
...
ingress_policing_burst: 100
ingress_policing_rate: 5000
...
type                : ""

Signed-off-by: Pieter Jansen van Vuuren <pieter.jansenvanvuuren@netronome.com>
Signed-off-by: Simon Horman <simon.horman@netronome.com>

lib/tc.c

@@ -1421,6 +1421,10 @@ parse_netlink_to_tc_flower(struct ofpbuf *reply, struct tc_flower *flower)
     flower->mask.eth_type = OVS_BE16_MAX;
     flower->prio = tc_get_major(tc->tcm_info);
 
+    if (flower->prio == TC_RESERVED_PRIORITY_POLICE) {
+        return 0;
+    }
+
     if (!flower->handle) {
         return EAGAIN;
     }