The hash function is needed to generate this a new Private Resolvable address.
This functionality is required to generate a table with a list of addresses
from the information in the bond table (See the getAddressesFromBondTable() API
in BLE API SecurityManager). However, this function is not exposed by the
nRF51 SDK to external code. This pull requests simply adds the function
declaration to the relevant .h file to make external use possible.