Rx: Add missing rx_packet.h includes

Rx: Add missing rx_packet.h includes

We no longer include rx_packet.h from rx.h, so rx_kcommon.h was not
picking up some packet-related definitions. Some files
(SOLARIS/rx_knet.c, IRIX/rx_knet.c) were using packet-related defines
(e.g. RX_HEADER_SIZE) while just including rx_kcommon.h. Include
rx_packet.h in those files to get the relevant definitions.

Change-Id: Ib012f295d8e324dd8b38eb0b89933eac392a9583
Reviewed-on: http://gerrit.openafs.org/6670
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>