Jira 858, Can't trigger BLEConnected, BLEDisconnected events, git 445
Jira 858, Can't trigger BLEConnected, BLEDisconnected events, git 445

Root casue:
  - The callback regiter before the begin and the begin
    reset the callback.

Code mods:
1. BLEPeripheral.cpp:
   - Remove clearing of callback register array at begin(). The
     array is cleared upon system initialization.

yashaswini-hanji/corelibs-arduino101,bigdinotech/corelibs-arduino101,sgbihu/corelibs-arduino101,01org/corelibs-arduino101,bigdinotech/corelibs-arduino101,sgbihu/corelibs-arduino101,sandeepmistry/corelibs-arduino101,yashaswini-hanji/corelibs-arduino101,sandeepmistry/corelibs-arduino101,yashaswini-hanji/corelibs-arduino101,bigdinotech/corelibs-arduino101,01org/corelibs-arduino101,01org/corelibs-arduino101,sandeepmistry/corelibs-arduino101,sgbihu/corelibs-arduino101