Fix bug in Static Route configuration path

ISSUE: Multiple equivalent static route configurations with different names not detected
CHANGE: In addStaticRoute() perform proper equality check on existing StaticRoute objects
        (using available StaticRoute compareTo() method) instead of checking on StaticRouteConfig
        objects which can never be positive as same name config is detected at the beginning of method

Change-Id: I51d2e1a641f612f5e79eb11063a868739a275209
Signed-off-by: Alessandro Boch <aboch@cisco.com>