ripd/ripngd: use common header for display command

Both rip and ripng can import routes from other protocols, e.g. ISIS.
But their header doesn't list the description for these abbreviations.

Let `show ip rip` (and `show ipv6 ripng`) uses the common header.

Before:
```
Codes: R - RIP, C - connected, S - Static, O - OSPF, B - BGP
Sub-codes:
      (n) - normal, (s) - static, (d) - default, (r) - redistribute,
      (i) - interface
```

After:
```
Codes: K - kernel route, C - connected, L - local, S - static,
       R - RIP, O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
       T - Table, v - VNC, V - VNC-Direct, A - Babel, F - PBR,
       f - OpenFabric, t - Table-Direct,
       > - selected route, * - FIB route, q - queued, r - rejected, b - backup
       t - trapped, o - offload failure

Sub-codes:
      (n) - normal, (s) - static, (d) - default, (r) - redistribute,
      (i) - interface
```

Signed-off-by: anlan_cs <[email protected]>

ripd/ripd.c

@@ -3053,8 +3053,7 @@ DEFUN (show_ip_rip,
 		return CMD_SUCCESS;
 	}
 
-	vty_out(vty,
-		"Codes: R - RIP, C - connected, S - Static, O - OSPF, B - BGP\n"
+	vty_out(vty, SHOW_ROUTE_V4_HEADER
 		"Sub-codes:\n"
 		"      (n) - normal, (s) - static, (d) - default, (r) - redistribute,\n"
 		"      (i) - interface\n\n"

ripngd/ripngd.c

@@ -2069,8 +2069,7 @@ DEFUN (show_ipv6_ripng,
 	}
 
 	/* Header of display. */
-	vty_out(vty,
-		"Codes: R - RIPng, C - connected, S - Static, O - OSPF, B - BGP\n"
+	vty_out(vty, SHOW_ROUTE_V6_HEADER
 		"Sub-codes:\n"
 		"      (n) - normal, (s) - static, (d) - default, (r) - redistribute,\n"
 		"      (i) - interface, (a/S) - aggregated/Suppressed\n\n"