monitor: Fix optstring to parse -b parameter
monitor: Fix optstring to parse -b parameter

Without the colon getopt ignores the parameter and optarg is always
NULL.

silent-snowman/bluez,mapfau/bluez,pkarasev3/bluez,pstglia/external-bluetooth-bluez,pstglia/external-bluetooth-bluez,silent-snowman/bluez,mapfau/bluez,silent-snowman/bluez,pkarasev3/bluez,ComputeCycles/bluez,ComputeCycles/bluez,mapfau/bluez,pstglia/external-bluetooth-bluez,pkarasev3/bluez,ComputeCycles/bluez,pstglia/external-bluetooth-bluez,pkarasev3/bluez,ComputeCycles/bluez,silent-snowman/bluez,mapfau/bluez