add option to rxperf to use rx_Readv() instead of rx_Read()
rx_Readv() is a bit "faster" than rx_Read() and typically used by most
afs transaction.
server% rxperf server
client% rxperf client -c send -s server
SEND: threads 1, times 100, bytes 1048576: 2073 msec
server% rxperf server -v
client% rxperf client -c send -s server
SEND: threads 1, times 100, bytes 1048576: 983 msec
Change-Id: I27b06dbbb61f2bc34fa91bcda3c6e046c787ff62
Reviewed-on: http://gerrit.openafs.org/2877
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>