pnfs/filelayout: add tracepoint to getdeviceinfo

While decoding filelayout getdeviceinfo received, print out the
information about the location of data servers (IPs).

Generic getdeviceinfo tracepoints prints the MDS's ip for the
dstaddr. In this patch, separate the MDS's address from the
DS's addresses.

Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>