[netdata] new API to get lowpan context IDs (#8870)

This commit adds `otNetDataGetNextLowpanContextInfo()` to iterate
through the list of LoWPAN Context entries in Thread Network Data
providing info about the prefix, its LoWPAN Context ID and Compress
flag (relating to `ContextTlv` sub-TLVs of `PrefixTlv`s in Network
Data).

This commit also updates CLI command `netdata show` to list the
context IDs in addition to prefixes, routes, and services.

tools/harness-thci/OpenThread.py

@@ -1694,7 +1694,7 @@ class OpenThreadTHCI(object):
     @watched
     def getNetworkData(self):
         lines = self.__executeCommand('netdata show')
-        prefixes, routes, services = [], [], []
+        prefixes, routes, services, contexts = [], [], [], []
         classify = None
 
         for line in lines:
@@ -1704,6 +1704,8 @@ class OpenThreadTHCI(object):
                 classify = routes
             elif line == 'Services:':
                 classify = services
+            elif line == 'Contexts:':
+                classify = contexts
             elif line == 'Done':
                 classify = None
             else:
@@ -1713,6 +1715,7 @@ class OpenThreadTHCI(object):
             'Prefixes': prefixes,
             'Routes': routes,
             'Services': services,
+            'Contexts': contexts,
         }
 
     @API

tools/otci/otci/otci.py

@@ -1570,7 +1570,16 @@ class OTCI(object):
                 routes_output.append(line)
 
         netdata['routes'] = self.__parse_routes(routes_output)
-        netdata['services'] = self.__parse_services(output)
+
+        services_output = []
+        while True:
+            line = output.pop(0)
+            if line == 'Contexts:':
+                break
+            else:
+                services_output.append(line)
+
+        netdata['services'] = self.__parse_services(services_output)
 
         return netdata