Windows: Export additional RX debugging variables from afsrpc.dll

Windows: Export additional RX debugging variables from afsrpc.dll

Export

   rxi_nRecvFrags                          @2008 DATA
   rxi_nSendFrags                          @2009 DATA
   rx_initReceiveWindow                    @2010 DATA
   rx_initSendWindow                       @2011 DATA
   rx_intentionallyDroppedPacketsPer100    @2012 DATA
   rx_intentionallyDroppedOnReadPer100     @2013 DATA

so they can be referenced from pthreaded builds of src/rx/test tools.
Exported variables must be present in both FREE and CHECKED builds.

Change-Id: Ia7f3ee0143679bab1ce74f71dc3a996cda1f18a8
Reviewed-on: http://gerrit.openafs.org/2779
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>