A few tweaks to the VL_RegisterAddrsAndKey text

Change-Id: I3cc8e42029ec1924c765853ae12a16beb513e979
Flesh out 'securing the callback channel'

Change-Id: Ifdb5c75c37c9ba3205a0ed7ee940bf4064d8a7b5
Add initials explicitly

Change-Id: Ib95e5969f765e6bc98f814ab9fad21606604d168