[netdata] adding NetworkData::Publisher (#6768)

This commit implements a new feature "Network Data Publisher" which
provides mechanisms to limit the number of similar entries (service
and/or prefix) in the Thread Network Data by monitoring the Network
Data and managing if or when to add or remove entries. This feature is
enabled using `OPENTHREAD_CONFIG_NETDATA_PUBLISHER_ENABLE` config, or
`NETDATA_PUBLISHER` in autoconf, or `OT_NETDATA_PUBLISHER` cmake
option.

This commit adds support for publishing DNS/SRP anycast/unicast
service, on-mesh prefix, and external route prefix entries.

When there is a request to publish an entry, the `Publisher` monitors
the Network Data and counts the number of similar entries. If there
are fewer entries than a desired target number, the entry is added
after a short random delay.

If there are too many similar entries, `Publisher` starts the process
of removing its own entry (again after some random wait time). When
removing entries, certain entries are preferred over others (e.g., an
entry from a router over one from an end-device or if they are from
the same type of node, the one with smaller RLOC16). If `Publisher`
determines that its own entry is a preferred one, it adds an extra
wait time before removing its entry. This gives higher chance for a
non-preferred entry from another device to be removed before removing
a preferred entry which helps towards quicker convergence of the
process to the desired number of entries.

On-mesh prefix and external route entries have a "preference" field.
When publishing such an entry, a matching entry in the network data is
counted only if its preference is same or higher than the entry's
preference. This ensures that a device with a higher preference entry
publishes its entry even when there are many lower preference similar
entries in the network data (potentially causing a lower preference
entry to be removed).

This commit also adds `test_netdata_publisher.py` to verify the
behavior of the `Publisher`.

examples/Makefile-simulation

@@ -60,6 +60,7 @@ LINK_RAW                       ?= 1
 MAC_FILTER                     ?= 1
 MTD_NETDIAG                    ?= 1
 NEIGHBOR_DISCOVERY_AGENT       ?= 1
+NETDATA_PUBLISHER              ?= 1
 PING_SENDER                    ?= 1
 REFERENCE_DEVICE               ?= 1
 SERVICE                        ?= 1

examples/README.md

@@ -48,6 +48,7 @@ This page lists the available common switches with description. Unless stated ot
 | MLR | OT_MLR | Enables Multicast Listener Registration feature for Thread 1.2. |
 | MTD_NETDIAG | OT_MTD_NETDIAG | Enables the TMF network diagnostics on MTDs. |
 | MULTIPLE_INSTANCE | OT_MULTIPLE_INSTANCE | Enables multiple OpenThread instances. |
+| NETDATA_PUBLISHER | OT_NETDATA_PUBLISHER | Enables support for Thread Network Data publisher. |
 | PING_SENDER | OT_PING_SENDER | Enables support for ping sender. |
 | OTNS | OT_OTNS | Enables support for [OpenThread Network Simulator](https://github.com/openthread/ot-ns). Enable this switch if you are building OpenThread for OpenThread Network Simulator. |
 | PLATFORM_UDP | OT_PLATFORM_UDP | Enables platform UDP support. |

examples/common-switches.mk

@@ -70,6 +70,7 @@ MLR                       ?= 0
 MTD_NETDIAG               ?= 0
 MULTIPLE_INSTANCE         ?= 0
 NEIGHBOR_DISCOVERY_AGENT  ?= 0
+NETDATA_PUBLISHER         ?= 0
 OTNS                      ?= 0
 PING_SENDER               ?= 1
 PLATFORM_UDP              ?= 0
@@ -265,6 +266,10 @@ ifeq ($(NEIGHBOR_DISCOVERY_AGENT),1)
 COMMONCFLAGS                   += -DOPENTHREAD_CONFIG_NEIGHBOR_DISCOVERY_AGENT_ENABLE=1
 endif
 
+ifeq ($(NETDATA_PUBLISHER),1)
+COMMONCFLAGS                   += -DOPENTHREAD_CONFIG_NETDATA_PUBLISHER_ENABLE=1
+endif
+
 ifeq ($(PING_SENDER),1)
 COMMONCFLAGS                   += -DOPENTHREAD_CONFIG_PING_SENDER_ENABLE=1
 endif