xenctx: Add command line options -b (--bytes-per-line) and -l (--lines)

xenctx: Add command line options -b (--bytes-per-line) and -l (--lines)

  -b <bytes>, --bytes-per-line <bytes>
                     change the number of bytes per line output for Stack.
                     (default 32) Note: rounded to native size (4 or 8 bytes).

This option allows you to change the width of the output line.  When
used with the -D option and/or -t, the output can be adjusted with
this to less then 80 columns.

  -l <lines>, --lines <lines>
                     change the number of lines output for Stack. (default 5)
                     Can be specified as MAX.  Note: Fewer lines will be output
                     if stack limit reached.

The default value show a reasonable amount of the raw stack.  The -S
option will output all of it one line at a time.  This can be used
to select something in the middle.

Signed-off-by: Don Slutz <dslutz@verizon.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>