pkg/nimble: add patch to fix pointer alignment issue.

Nimble contains a couple of casts that discard alignment information.
This causes a warning with clang's -Wno-address-of-packed-member.

A previous PR (#10503) supressed that warning. This commit re-enables
them and provides a patch to fix the offending code.

The fix has been submitted upstream, see
https://github.com/apache/mynewt-nimble/pull/252