c/util: Making util/crypto.h a public header

Change-Id: Ie63d3b5b206ae7e027e11077b6c0a039ed75eb92
face-management-protocol: Fixing small bug with ForwardingEntry

The daemon always expects Prefix entry, even though it is defined
optional in the protocol.

Change-Id: I4ade13897af8e47944be2384a2fc116959e50d15