Use EXTRACT_16BITS() and EXTRACT_32BITS() to fetch integral values.

Use EXTRACT_16BITS() and EXTRACT_32BITS() to fetch integral values.

Use EXTRACT_16BITS() and EXTRACT_32BITS() to fetch 16-bit and 32-bit
big-endian quantities from the packet, as there's no guarantee that a
given 16-bit quantity will be aligned on a 2-byte boundary or that a
given 32-bit quantity will be aligned on a 4-byte boundary, nor is there
a guarantee that unaligned accesses will succeed (they might trap, or
they might not fetch an unaligned quantity).