Revert "Endian optimization bugfix to model.c"

This reverts commit 8f8f2d8f5e1df7aadb9af7ca869f07e49ee4c5a3.
Revert "Endian optimizations #1"

This reverts commit 219bfbfd5a0490107b2d377554ac9257f7c4229e.
Define MSB_FIRST for big endian targets