bt_shell: fix command bt advertise valid argument count

Changed number of valid arguments from two required to
one required and one optional.

Command can be called with required <type: off, on, scan, nconn>
and optional <mode: discov, non_discov>".

Signed-off-by: Jakub Rzeszutko <jakub.rzeszutko@nordicsemi.no>
diff --git a/subsys/bluetooth/shell/bt.c b/subsys/bluetooth/shell/bt.c
index 791348d..62ab2a2 100644
--- a/subsys/bluetooth/shell/bt.c
+++ b/subsys/bluetooth/shell/bt.c
@@ -1333,7 +1333,7 @@
 		      cmd_scan, 3, 0),
 	SHELL_CMD_ARG(advertise, NULL,
 		      "<type: off, on, scan, nconn> <mode: discov, non_discov>",
-		      cmd_advertise, 3, 0),
+		      cmd_advertise, 2, 1),
 #if defined(CONFIG_BT_CONN)
 	SHELL_CMD_ARG(connect, NULL, HELP_ADDR_LE, cmd_connect_le, 3, 0),
 	SHELL_CMD_ARG(disconnect, NULL, HELP_NONE, cmd_disconnect, 1, 0),