nimble/att: Use packed struct for receiving Write Command
nimble/att: Use packed struct for receiving Write Command

Use packed structure to map it to received mbuf instead of using
dedicated parsing function. Modern compilers generate effective code
in such case anyway.

X-Original-Commit: 3876f10f11473407fb8326cacd15956105fc10b4

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