ifupdownaddons: iproute2: add optional refresh flag to addr get api

Ticket:
Reviewed By: trivial
Testing Done: tested address gets with refresh flag + ran ssim test testifupdown2.py

- also fixes refresh flag handling in cache _addr_fill function
- this api can be used to get addresses from the cache by first
refreshing the cache. So the caller gets fresh running addresses.
(its not used right now but came up during the need to re-apply
addresses for ipv6 vrf slaves since their addresses may disappear)

ifupdownaddons/iproute2.py

@@ -132,10 +132,10 @@ class iproute2(utilsBase):
         """
 
         linkout = {}
-        if iproute2._cache_fill_done: return
+        if iproute2._cache_fill_done and not refresh: return
         try:
             # Check if ifacename is already full, in which case, return
-            if ifacename:
+            if ifacename and not refresh:
                 linkCache.get_attr([ifacename, 'addrs']) 
                 return
         except:
@@ -331,8 +331,9 @@ class iproute2(utilsBase):
             # ignore errors
             pass
 
-    def addr_get(self, ifacename, details=True):
-        addrs = self._cache_get('addr', [ifacename, 'addrs'])
+    def addr_get(self, ifacename, details=True, refresh=False):
+        addrs = self._cache_get('addr', [ifacename, 'addrs'],
+                                refresh=refresh)
         if not addrs:
             return None
         if details: