BLE Host - Add comment about ltk endianness.
BLE Host - Add comment about ltk endianness.

X-Original-Commit: 0b120257b855f08225b9dc5fce097eea94971da3

apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble