client: Add advertise command

This adds advertise command which uses org.bluez.LEAdvertisingManager1 to
add an advertising instance:

[bluetooth]# advertise
broadcast   off         on          peripheral
[bluetooth]# advertise on
Advertising object registered

@ Advertising Added: 1
< HCI Command: LE Set Advertising Data (0x08|0x0008) plen 32
        Length: 3
        Flags: 0x02
          LE General Discoverable Mode

[bluetooth]# advertise off
Advertising object unregistered

@ Advertising Removed: 1
< HCI Command: LE Set Advertise Enable (0x08|0x000a) plen 1
        Advertising: Disabled (0x00)
3 files changed