pkg/nimble: Add ble_hs_stop.c to makefile

[ccollins476ad]

Contribution description

This file (ble_hs_stop.c) was added to NimBLE in this PR: apache/mynewt-nimble#216. This PR adds an entry for this file to the pkg/nimble/nimble.host.mk Makefile.

Without this change, an attempt to build the nimble package fails with a linker error, as seen here: https://travis-ci.org/apache/mynewt-nimble/jobs/458153788

Testing procedure

Simply ensure the nimble_gatt example builds, e.g.,

cd examples/nimble_gatt && make

Issues/PRs references

[kaspar030]

@ccollins476ad welcome to the RIOT community and thanks for your contribution!

The nimble commit currently linked in pkg/nimble/Makefile doesn't include this file. I guess the fix would be necessary when bumping the nimble version?

[ccollins476ad]

Thanks, @kaspar030. I am not especially familiar with RIOT. It seems I should have done a bit more research before submitting this PR! The failing Travis jobs in the nimble repo were the motivation for this PR. I was a bit surprised that a change to a foreign repo (nimble) could break RIOT; it seems I should have followed up on this suspicion.

The Murdock job for this PR is failing because it can't find ble_hs_stop.c, which makes sense in light of your comment above. I think it makes the most sense if I close this PR and investigate the proper way to fix the nimble travis failures.

Thanks again.