qcacmn: DFS code cleanup

* Remove nif and sif keyword.
* Combine nif_dfs_detach and sif_dfs_detach.
* Combine nif_dfs_attach and dfs_attach.

Change-Id: Ibf4638a64fac976846bfcb1eae91f3f3bb3e994e
CRs-Fixed: 2071164
15 files changed