change static rt expiry timer max value (#14397)

Why I did it
Change static route expiry timer max timeout value from 1800 to 172800.
To keep same value range as defined in sonic-restapi/sonic_api.yaml

How I did it
How to verify it
apply change to bgpcfd, restart bgp container see if the value take action.

src/sonic-bgpcfgd/bgpcfgd/static_rt_timer.py

@@ -12,7 +12,8 @@ class StaticRouteTimer(object):
 
     DEFAULT_TIMER = 180
     DEFAULT_SLEEP = 60
-    MAX_TIMER     = 1800
+    # keep same range as value defined in sonic-restapi/sonic_api.yaml
+    MAX_TIMER     = 172800
 
     def set_timer(self):
         """ Check for custom route expiry time in STATIC_ROUTE_EXPIRY_TIME """
@@ -56,3 +57,4 @@ class StaticRouteTimer(object):
                 time.sleep(self.DEFAULT_SLEEP)
                 if time.time() - self.start >= self.DEFAULT_TIMER:
                     self.alarm()
+