allow func_len to be 0 in sonic-srv6.yang (sonic-net#611)

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#### Why I did it

Previously, we didn't allow the func_len to zero in YANG model, which conflicts with our use case.

##### Work item tracking
- Microsoft ADO **(number only)**:

#### How I did it

Change the lower bound of the func_len's range.

#### How to verify it

Configure a locator entry in CONFIG_DB and then do a config reload.

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Author: mssonicbld

src/sonic-yang-models/yang-models/sonic-srv6.yang

@@ -35,7 +35,7 @@ module sonic-srv6 {
                     type uint8 {
                         range "1..128";
                     }
-                    
+
                     default 32;
                 }
 
@@ -49,7 +49,7 @@ module sonic-srv6 {
 
                 leaf func_len {
                     type uint8 {
-                        range "1..128";
+                        range "0..128";
                     }
 
                     default 16;
@@ -127,6 +127,6 @@ module sonic-srv6 {
                                   substring-before(/srv6:sonic-srv6/SRV6_MY_LOCATORS/SRV6_MY_LOCATORS_LIST[current()/locator]/prefix, "::"))';
             }
         }
-        
+
     }
 }