[Coverity CID :190970]Uninitialized variables in /subsys/bluetooth/shell/ll.c

[mandarcthorat1]

Static code scan issues seen in File: /subsys/bluetooth/shell/ll.c
Category: Uninitialized variables
Function: cmd_advx
Component: Bluetooth
CID: 190970
Please fix or provide comments to square it off in coverity in the link: https://scan9.coverity.com/reports.htm#v32951/p12996

[ceolin]

#13975