ICMP.3d specifies unused bytes instead of bits

[Smfakhoury]

The ICMP specification indicates that there should be a number of unused bits for some messages.

The number of unused bits vary:

• Destination Unreachable Message: 32 bits
• Time Exceeded Message: 32 bits
• Parameter Problem Message: 24 bits
• Source Quench Message: 32 bits

The current ICMP.3d spec specifies these as byte fields not bit fields:

typedef struct _UNUSED_BYTES (UINT32 len)
{
    ZeroByte    Bytes[len];
} UNUSED_BYTES;

For example in parameter problem:

typedef struct _PARAMETER_PROBLEM_MESSAGE
{
    UINT8                     Code
    {
        Code == 0
    };
    UINT16BE                  Checksum;
    UINT8                     Pointer;  //Valid only if code is 0, is there something to check?
    UNUSED_BYTES(24)          Unused;
    IP_HEADER_AND_DATAGRAM    OriginalMsg;
} PARAMETER_PROBLEM_MESSAGE;

Or in Source quench:

typedef struct _SOURCE_QUENCH_MESSAGE
{
    UINT8                     Code
    {
        Code == 0
    };
    UINT16BE                  Checksum;
    UNUSED_BYTES(32)          Unused;
    IP_HEADER_AND_DATAGRAM    OriginalMsg;
} SOURCE_QUENCH_MESSAGE;

The 3d code could be modified to:

typedef struct _SOURCE_QUENCH_MESSAGE
{
...
    UINT32BE          Unused;
....
} 

And

typedef struct _PARAMETER_PROBLEM_MESSAGE
{
...
    UINT8          Unused[3]; 
....
}