nodelist: Make HSv3 protover magic numbers a bit more readable.

src/or/nodelist.c

@@ -722,7 +722,7 @@ node_supports_v3_hsdir(const node_t *node)
       return 0;
     }
     return protocol_list_supports_protocol(node->ri->protocol_list,
-                                           PRT_HSDIR, 2);
+                                           PRT_HSDIR, PROTOVER_HSDIR_V3);
   }
   tor_assert_nonfatal_unreached_once();
   return 0;
@@ -743,7 +743,7 @@ node_supports_ed25519_hs_intro(const node_t *node)
       return 0;
     }
     return protocol_list_supports_protocol(node->ri->protocol_list,
-                                           PRT_HSINTRO, 4);
+                                           PRT_HSINTRO, PROTOVER_HS_INTRO_V3);
   }
   tor_assert_nonfatal_unreached_once();
   return 0;

src/or/protover.h

@@ -17,6 +17,11 @@
 /* This is a guess. */
 #define FIRST_TOR_VERSION_TO_ADVERTISE_PROTOCOLS "0.2.9.3-alpha"
 
+/** The protover version number that signifies HSDir support for HSv3 */
+#define PROTOVER_HSDIR_V3 2
+/** The protover version number that signifies HSv3 intro point support */
+#define PROTOVER_HS_INTRO_V3 4
+
 /** List of recognized subprotocols. */
 typedef enum protocol_type_t {
   PRT_LINK,