Fix 500 error  during router-update for dvr routers

This was caused because the l3 service plugin was
erroneously calling a method on self, whereas the
method is implemented by the core plugin.

Closes-bug: #1352786

Change-Id: I0746eee314730370b2df4bef6d9fd41680e2e3d1
Merge "Fix 500 error  during router-update for dvr routers"