Print rxdebug statistics as unsigned values

Print rxdebug statistics as unsigned values

bytesSent and bytesReceived are unsigned.  Print them as such
to avoid printing negative numbers for large values.  This is
already the case in the master branch.

Bug reported by jakllsch on IRC

Change-Id: If2c5d9cfebf11691d73b3d6bfd73deb6b61ada8e
Reviewed-on: http://gerrit.openafs.org/1657
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit a123d4ab988c6a8cc51b864ea1d02a70b2770bf3)