Remove extra newline from spa_set_allocator().

zfs_dbgmsg() does not need newline at the end of the message.

While there, slightly update/sync FreeBSD __dprintf().

Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by:	Alexander Motin <mav@FreeBSD.org>
Sponsored by:	iXsystems, Inc.
Closes openzfs#16536

Author: amotin

module/os/freebsd/zfs/zfs_debug.c

@@ -218,12 +218,19 @@ __dprintf(boolean_t dprint, const char *file, const char *func,
 	}
 
 	/*
-	 * Get rid of trailing newline.
+	 * Get rid of trailing newline for dprintf logs.
 	 */
-	nl = strrchr(buf, '\n');
-	if (nl != NULL)
-		*nl = '\0';
+	if (dprint && buf[0] != '\0') {
+		nl = &buf[strlen(buf) - 1];
+		if (*nl == '\n')
+			*nl = '\0';
+	}
 
+	/*
+	 * To get this data:
+	 *
+	 * $ sysctl -n kstat.zfs.misc.dbgmsg
+	 */
 	__zfs_dbgmsg(buf);
 
 	kmem_free(buf, size);

module/zfs/metaslab.c

@@ -1679,7 +1679,7 @@ spa_set_allocator(spa_t *spa, const char *allocator)
 	int a = spa_find_allocator_byname(allocator);
 	if (a < 0) a = 0;
 	spa->spa_active_allocator = a;
-	zfs_dbgmsg("spa allocator: %s\n", metaslab_allocators[a].msop_name);
+	zfs_dbgmsg("spa allocator: %s", metaslab_allocators[a].msop_name);
 }
 
 int