BLE Host - reuse exec-write-req mbuf for rsp.
BLE Host - reuse exec-write-req mbuf for rsp.

The response has the same contents as the request; only the op code is
different.  By reusing the mbuf, it makes failure due to mbuf exhaustion
less likely.

X-Original-Commit: 5877bada3719bf1d31cad810a9c58f27c3c25e3f

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