Add Kconfig configuration to conditionally enable LE Ping
feature in the Controller.
This will save CPU time, flash and RAM, if this feature is
not desired.
Change-id: I5fbbdbe8f45ac01c9b0d7b11e002a0d1db4d272e
Signed-off-by: Vinayak Chettimada <vinayak.kariappa.chettimada@nordicsemi.no>