pcap: Update the 'File Header' diagram about Major/Minor Versions

Use the same format as in the 'Section Header Block Format' pcapng
diagram.

This also indicates the positions of the two fields Major Version and
Minor Version, two bytes after the Magic Number field and two bytes
after the previous.

Moreover:
Add the hexa 16-bit values for both endian orders:
  "(big-endian 0x00 0x02 or little-endian 0x02 0x00)" for Major Version.
  "(big-endian 0x00 0x04 or little-endian 0x04 0x00)" for Minor Version.

s/little endian/little-endian/
s/big endian/big-endian/

draft-ietf-opsawg-pcap.md

@@ -68,7 +68,7 @@ A capture file begins with a File Header, followed by zero or more
 Packet Records, one per packet.
 
 All fields in the File Header and in the headers of Packet Records will
-always be written according to the characteristics (little endian / big
+always be written according to the characteristics (little-endian / big-
 endian) of the machine that is writing the file.  This refers to all the
 fields that are written as numbers and that span over two or more
 octets.
@@ -85,12 +85,12 @@ The File Header has the following format, with the octet offset of
 fields shown to the left of the field:
 
 ~~~~
+                           1                   2                   3
+       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     0 |                          Magic Number                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-    4 |          Major Version        |
-      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-    6 |          Minor Version        |
+    4 |         Major Version         |         Minor Version         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     8 |                           Reserved1                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
@@ -119,7 +119,8 @@ machines, and to heuristically identify pcap files.
 
 Major Version (16 bits):
 : an unsigned value, giving the number of the current major version of
-the format.  The value for the current version of the format is 2.  This
+the format.  The value for the current version of the format is 2
+(big-endian 0x00 0x02 or little-endian 0x02 0x00).  This
 value should change if the format changes in such a way that code that
 reads the new format could not read the old format (i.e., code to read
 both formats would have to check the version number and use different
@@ -128,7 +129,8 @@ not read the new format.
 
 Minor Version (16 bits):
 : an unsigned value, giving the number of the current minor version of
-the format.  The value for the current version of the format is 4.
+the format.  The value for the current version of the format is 4
+(big-endian 0x00 0x04 or little-endian 0x04 0x00).
 This value should change if the format changes in such a way that code
 that reads the new format could read the old format without checking the
 version number but code that reads the old format could not read all