Support Different Number of Max Children (#872)

* Add support for setting child max, for platforms that define a different maximum number of supported children.

tests/scripts/thread-cert/Cert_5_1_07_MaxChildCount.py

@@ -52,6 +52,7 @@ class Cert_5_1_07_MaxChildCount(unittest.TestCase):
         self.nodes[ROUTER].add_whitelist(self.nodes[LEADER].get_addr64())
         self.nodes[ROUTER].enable_whitelist()
         self.nodes[ROUTER].set_router_selection_jitter(1)
+        self.nodes[ROUTER].set_max_children(10)
 
         self.nodes[ED].set_panid(0xface)
         self.nodes[ED].set_mode('rsn')

tests/scripts/thread-cert/node.py

@@ -345,6 +345,11 @@ class Node:
         self.send_command(cmd)
         self.pexpect.expect('Done')
 
+    def set_max_children(self, number):
+        cmd = 'childmax %d' % number
+        self.send_command(cmd)
+        self.pexpect.expect('Done')
+
     def get_weight(self):
         self.send_command('leaderweight')
         i = self.pexpect.expect('(\d+)\r\n')