gpcdr kernel module

Cray's gpcdr kernel module is the source of the aries_linkstatus sampler metrics. It is also the source of Cray Gemini traffic and stall metrics in cray_gemini_r_sampler. While it can be the source of the Cray Aries traffic and stall metrics in the cray_aries_r_sampler, it is recommended that you turn off these metrics in that sampler and instead get the traffic and stall metrics from the aries_nic_mmr and aries_rtr_mmr_samplers instead, which do not use gpcdr, but rather use the gpcd interface to read the counter data more efficiently (there is no way to get the linkstatus metrics via the gpcd interface, so gpcdr must be used for those metrics).