Update existing fallthrough comments for GCC 7

The stricter warning levels (-Wimplicit-fallthrough=4) require all-caps
FALLTHROUGH, so update the existing comments to match.

Change-Id: I5f8608101cad31d8ea8e84d48604397f98400e87
Signed-off-by: Daniel Verkamp <daniel.verkamp@intel.com>
Reviewed-on: https://review.gerrithub.io/363491
Tested-by: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>

lib/bdev/nvme/blockdev_nvme.c

@@ -584,7 +584,7 @@ timeout_cb(void *cb_arg, struct spdk_nvme_ctrlr *ctrlr,
 			SPDK_ERRLOG("Unable to send abort. Resetting.\n");
 		}
 
-	/* Fallthrough */
+	/* FALLTHROUGH */
 	case TIMEOUT_ACTION_RESET:
 		rc = spdk_nvme_ctrlr_reset(ctrlr);
 		if (rc) {

lib/event/reactor.c

@@ -441,7 +441,7 @@ spdk_reactor_start(struct spdk_reactor *reactor)
 		switch (rte_eal_get_lcore_state(reactor->lcore)) {
 		case FINISHED:
 			rte_eal_wait_lcore(reactor->lcore);
-		/* drop through */
+		/* FALLTHROUGH */
 		case WAIT:
 			rte_eal_remote_launch(_spdk_reactor_run, (void *)reactor, reactor->lcore);
 			break;

lib/net/sock.c

@@ -184,7 +184,7 @@ retry:
 						    "Verify IP address in config file "
 						    "and make sure setup script is "
 						    "run before starting spdk app.\n", ip);
-				/* fallthrough */
+				/* FALLTHROUGH */
 				default:
 					/* try next family */
 					close(sock);