Documentation: e1000: Fix docs build error

Recent patch updated e1000 docs to rst format.  Docs build (`make
htmldocs`) is currently failing due to this file with error:

        (SEVERE/4) Unexpected section title.

This is because a section of the file is indented 2 spaces.  Build error
can be cleared by aligning the text with column 0.  While we are changing
these lines we can make sure line length does not exceed 72, that
newlines following headings are uniform, and that full stops are
followed by two spaces.

Align text with column 0, limit line length to 72, ensure two spaces
follow all full stops, ensure uniform use of newlines after heading.

Fixes commit (228046e7 Documentation: e1000: Update kernel documentation)

CC: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Tobin C. Harding <me@tobin.cc>
Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>