Add bond/bridge YAML emitter

Add int_to_mode() and int_to_lb() in config/bondethernet.py to map back
the retrieved values from VPP into their config strings.

Implement bond and bridge settings dumper, dumping all settings even if
they are default. This helps the user understand the configurable
options.

config/test_bondethernet.py

@@ -49,6 +49,15 @@ class TestBondEthernetMethods(unittest.TestCase):
         self.assertEqual(5, bondethernet.mode_to_int("lacp"))
         self.assertEqual(-1, bondethernet.mode_to_int("not-exist"))
 
+    def test_int_to_mode(self):
+        self.assertEqual("round-robin", bondethernet.int_to_mode(1))
+        self.assertEqual("active-backup", bondethernet.int_to_mode(2))
+        self.assertEqual("xor", bondethernet.int_to_mode(3))
+        self.assertEqual("broadcast", bondethernet.int_to_mode(4))
+        self.assertEqual("lacp", bondethernet.int_to_mode(5))
+        self.assertEqual("", bondethernet.int_to_mode(0))
+        self.assertEqual("", bondethernet.int_to_mode(6))
+
     def test_get_lb(self):
         self.assertEqual('l34', bondethernet.get_lb(self.cfg, "BondEthernet0"))
         self.assertEqual('l2', bondethernet.get_lb(self.cfg, "BondEthernet1"))
@@ -62,3 +71,12 @@ class TestBondEthernetMethods(unittest.TestCase):
         self.assertEqual(4, bondethernet.lb_to_int("broadcast"))
         self.assertEqual(5, bondethernet.lb_to_int("active-backup"))
         self.assertEqual(-1, bondethernet.lb_to_int("not-exist"))
+
+    def test_int_to_lb(self):
+        self.assertEqual("l2", bondethernet.int_to_lb(0))
+        self.assertEqual("l34", bondethernet.int_to_lb(1))
+        self.assertEqual("l23", bondethernet.int_to_lb(2))
+        self.assertEqual("round-robin", bondethernet.int_to_lb(3))
+        self.assertEqual("broadcast", bondethernet.int_to_lb(4))
+        self.assertEqual("active-backup", bondethernet.int_to_lb(5))
+        self.assertEqual("", bondethernet.int_to_lb(-1))