MFC 308056: Fix formatting of tables.

Specifically, use .Ta instead of tabs to separate column entries. While
here fix a few other things:

• Use .Sy for all column headers (previously only the first column header was bold)
• Use .Dv to markup constants used for MIB names.
• Use "1234" and "4321" for the byte order descriptions without thousands separators.
• Mark up header files in the first table with .In.