nimble: convert HCI error codes to hex
nimble: convert HCI error codes to hex

Spec defines these error codes as hexes so it's easier to read
and compare them as hexes.

X-Original-Commit: 7426bfb377cf892bc71cea8f2d8f2bca3a6aa0d5

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