net: netrom: Fix fall-through warnings for Clang

In preparation to enable -Wimplicit-fallthrough for Clang, fix multiple
warnings by explicitly adding multiple break statements instead of
letting the code fall through to the next case.

Link: KSPP#115
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Author: GustavoARSilva

net/netrom/nr_route.c

@@ -266,6 +266,7 @@ static int __must_check nr_add_node(ax25_address *nr, const char *mnemonic,
 		fallthrough;
 	case 2:
 		re_sort_routes(nr_node, 0, 1);
+		break;
 	case 1:
 		break;
 	}
@@ -359,6 +360,7 @@ static int nr_del_node(ax25_address *callsign, ax25_address *neighbour, struct n
 					fallthrough;
 				case 1:
 					nr_node->routes[1] = nr_node->routes[2];
+					fallthrough;
 				case 2:
 					break;
 				}
@@ -482,6 +484,7 @@ static int nr_dec_obs(void)
 					fallthrough;
 				case 1:
 					s->routes[1] = s->routes[2];
+					break;
 				case 2:
 					break;
 				}
@@ -529,6 +532,7 @@ void nr_rt_device_down(struct net_device *dev)
 							fallthrough;
 						case 1:
 							t->routes[1] = t->routes[2];
+							break;
 						case 2:
 							break;
 						}