afspag version of rx_knet.o

afspag version of rx_knet.o

in order to correctly generate KBUILD_MODNAME, each object
file needs to be built only once. in this case it matters because the
pr_debug macro, called as a result of including errqueue.h, needs it
and things which depend on it, and when it's built into 2 .kos,
the wrong thing happens.

Change-Id: I85be7a3322fd179ef75fe14a90c9e7592e542ed1
Reviewed-on: http://gerrit.openafs.org/2435
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>