Root-Canal: Explicitly set initial advertising parameters

The Core specification does not require that
LE Set Advertising Parameters be called before
LE Set Advertising Enable; instead default values
are specified for all advertising parameters.

This change lets hosts enable advertising
using the default parameters.

Test: PTS test GATT/SR/GAD/BV-01-C against Eiffel stack
Change-Id: I5d429d40eddb7ceff3d33a7d864db48a8f2ed3e9