Reading 8- or 16-bit attributes from big-endian device returns 0

[pjzander-signify]

Problem

When reading an 8- or 16-bit attribute from a big endian device the value is 0, despite that defaults other than 0 are defined.

The defaults of these attributes are defined in a zap-file and from that a header file is generated (endpoint_config.h).
This header file contains structures that are used by the software to read cluster information and the attributes of these clusters.
The value of these attributes are stored in a union that also contains 2 pointers:
typedef union { uint8_t * ptrToDefaultValue; uint16_t defaultValue; EmberAfAttributeMinMaxValue * ptrToMinMaxValue; } EmberAfDefaultOrMinMaxAttributeValue;

A generated default value is compiled into that union using an explicit type cast to a pointer.
Example:
{ (uint8_t *) 3 } }
In a 32-bit little-endian the memory layout will be:
03 00 00 00
The 16-bit defaultValue (the first 2 bytes) will have the value 3, which is correct.

In a 32-bit big-endian system the layout will be:
00 00 00 03
The 16-bit defaultValue (the first 2 bytes) will have the value 0, which is not correct.

Proposed Solution

Use a structure for the defaultValue, and that structure has the same size as a pointer.
Then use alignment bits to always align the 16-bit defaultValue with the least-significant-bits of the pointer.

[pjzander-signify]

I will create a new pull request