The new column is the difference between TX and RX time. This can be useful
to check fiber length (or just to see the data is good before feeding
it to the python scripts).

Suggested by Peter.

   wrc# mode abscal start
   PTP stop
   Locking PLL...
   PTP start
   t4.phase is already corrected for bitslide
   t1:                     t4:                  bitslide: 4800
         sec.       ns.pha       sec.       ns.pha
   wrc# 000000013 000082656 000 000000013 000082995 118         339.118
   000000014 000075536 000 000000014 000075875 117         339.117
   000000015 000084512 000 000000015 000084851 115         339.115
   000000016 000077008 000 000000016 000077347 115         339.115
   000000017 000085280 000 000000017 000085619 117         339.117
   000000018 000079984 000 000000018 000080323 118         339.118
   000000019 000058784 000 000000019 000059123 115         339.115
   000000020 000057424 000 000000020 000057763 118         339.118
   000000021 000056768 000 000000021 000057107 115         339.115
   000000022 000056240 000 000000022 000056579 118         339.118
   000000023 000060800 000 000000023 000061139 115         339.115
   000000024 000073200 000 000000024 000073539 118         339.118
   000000025 000058816 000 000000025 000059155 115         339.115
   000000026 000082896 000 000000026 000083235 118         339.118
   000000027 000070880 000 000000027 000071219 118         339.118
   000000028 000084624 000 000000028 000084963 115         339.115
   000000029 000076672 000 000000029 000077011 115         339.115
   000000030 000084848 000 000000030 000085187 115         339.115
   000000031 000075872 000 000000031 000076211 115         339.115
   000000032 000057488 000 000000032 000057827 117         339.117
   000000033 000081568 000 000000033 000081907 117         339.117
   000000034 000056080 000 000000034 000056419 118         339.118
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>