some sub-types and constants applicable to GapAdvertisingParams could be extracted to BLEProtocol.h

[rgrover]

AdvertisingType_t can encapsulated into a struct and possibly be moved.
we can create types for advertising interval and timeout.
constants defining min and max for the interval and timeout could be extracted.

[andresag01]

@rgrover: If we are thinking of moving the constants defining min and max for the interval and timeout perhaps we should also consider moving the constants in GapScanningParams. See https://github.com/ARMmbed/ble/blob/master/ble/GapScanningParams.h#L22.

[ciarmcom]

ARM Internal Ref: IOTSFW-1421

[rgrover]

@andresag01 yes, that's valid. Thanks for bringing this up.