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>
1 file changed