Set preference for forced mgmt routes (#5844)

When forced mgmt routes are present, the issue fixed as part of #5754 is not complete. 
Added a preference(priority) field to forced mgmt route ip rules

Author: prsunny

files/image_config/interfaces/interfaces.j2

@@ -80,14 +80,14 @@ iface eth0 {{ 'inet' if prefix | ipv4 else 'inet6' }} static
     up ip {{ '-4' if prefix | ipv4 else '-6' }} route add {{ prefix | network }}/{{ prefix | prefixlen }} dev eth0 table {{ vrf_table }}
     up ip {{ '-4' if prefix | ipv4 else '-6' }} rule add pref 32765 from {{ prefix | ip }}/{{ '32' if prefix | ipv4 else '128' }} table {{ vrf_table }}
 {% for route in MGMT_INTERFACE[(name, prefix)]['forced_mgmt_routes'] %}
-    up ip rule add to {{ route }} table {{ vrf_table }}
+    up ip rule add pref 32764 to {{ route }} table {{ vrf_table }}
 {% endfor %}
     # management port down rules
     pre-down ip {{ '-4' if prefix | ipv4 else '-6' }} route delete default via {{ MGMT_INTERFACE[(name, prefix)]['gwaddr'] }} dev eth0 table {{ vrf_table }}
     pre-down ip {{ '-4' if prefix | ipv4 else '-6' }} route delete {{ prefix | network }}/{{ prefix | prefixlen }} dev eth0 table {{ vrf_table }}
     pre-down ip {{ '-4' if prefix | ipv4 else '-6' }} rule delete pref 32765 from {{ prefix | ip }}/{{ '32' if prefix | ipv4 else '128' }} table {{ vrf_table }}
 {% for route in MGMT_INTERFACE[(name, prefix)]['forced_mgmt_routes'] %}
-    pre-down ip rule delete to {{ route }} table {{ vrf_table }}
+    pre-down ip rule delete pref 32764 to {{ route }} table {{ vrf_table }}
 {% endfor %}
 {# TODO: COPP policy type rules #}
 {% endfor %}

src/sonic-config-engine/tests/sample_output/py2/mvrf_interfaces

@@ -32,10 +32,14 @@ iface eth0 inet static
     up ip -4 route add default via 10.0.0.1 dev eth0 table 5000 metric 201
     up ip -4 route add 10.0.0.0/24 dev eth0 table 5000
     up ip -4 rule add pref 32765 from 10.0.0.100/32 table 5000
+    up ip rule add pref 32764 to 11.11.11.11 table 5000
+    up ip rule add pref 32764 to 22.22.22.0/23 table 5000
     # management port down rules
     pre-down ip -4 route delete default via 10.0.0.1 dev eth0 table 5000
     pre-down ip -4 route delete 10.0.0.0/24 dev eth0 table 5000
     pre-down ip -4 rule delete pref 32765 from 10.0.0.100/32 table 5000
+    pre-down ip rule delete pref 32764 to 11.11.11.11 table 5000
+    pre-down ip rule delete pref 32764 to 22.22.22.0/23 table 5000
 iface eth0 inet6 static
     address 2603:10e2:0:2902::8
     netmask 64

src/sonic-config-engine/tests/sample_output/py3/mvrf_interfaces

@@ -32,10 +32,14 @@ iface eth0 inet static
     up ip -4 route add default via 10.0.0.1 dev eth0 table 5000 metric 201
     up ip -4 route add 10.0.0.0/24 dev eth0 table 5000
     up ip -4 rule add pref 32765 from 10.0.0.100/32 table 5000
+    up ip rule add pref 32764 to 11.11.11.11 table 5000
+    up ip rule add pref 32764 to 22.22.22.0/23 table 5000
     # management port down rules
     pre-down ip -4 route delete default via 10.0.0.1 dev eth0 table 5000
     pre-down ip -4 route delete 10.0.0.0/24 dev eth0 table 5000
     pre-down ip -4 rule delete pref 32765 from 10.0.0.100/32 table 5000
+    pre-down ip rule delete pref 32764 to 11.11.11.11 table 5000
+    pre-down ip rule delete pref 32764 to 22.22.22.0/23 table 5000
 iface eth0 inet6 static
     address 2603:10e2:0:2902::8
     netmask 64

src/sonic-config-engine/tests/t0-sample-graph-mvrf.xml

@@ -393,6 +393,11 @@
       <a:DeviceMetadata>
         <a:Name>switch-t0</a:Name>
         <a:Properties>
+          <a:DeviceProperty>
+            <a:Name>ForcedMgmtRoutes</a:Name>
+            <a:Reference i:nil="true"/>
+            <a:Value>11.11.11.11;22.22.22.0/23</a:Value>
+          </a:DeviceProperty>
           <a:DeviceProperty>
             <a:Name>ErspanDestinationIpv4</a:Name>
             <a:Reference i:nil="true"/>