nimble/host: Add support for stopping advertising instance
nimble/host: Add support for stopping advertising instance

This allows to stop enabled advertising instance.

X-Original-Commit: 51a3c6785e5ad9c3a32565c160093f67cfa10456

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