LU-9480 lnet: add "lnetctl peer list"

LU-9480 lnet: add "lnetctl peer list"

Add IOC_LIBCFS_GET_PEER_LIST to obtain a list of the primary
NIDs of all peers known to the system. The list is written
into a userspace buffer by the kernel. The typical usage is
to make a first call to determine the required buffer size,
then a second call to obtain the list.

Extend the "lnetctl peer" set of commands with a "list"
subcommand that uses this interface.

Modify the IOC_LIBCFS_GET_PEER_NI ioctl (which is new in the
Multi-Rail code) to use a NID to indicate the peer to look
up, and then pass out the data for all NIDs of that peer.

Re-implement "lnetctl peer show" to obtain the list of NIDs
using IOC_LIBCFS_GET_PEER_LIST followed by one or more
IOC_LIBCFS_GET_PEER_NI calls to get information for each
peer.

Make sure to copy the structure from kernel space to
user space even if the ioctl handler returns an error.
This is needed because if the buffer passed in by the
user space is not big enough to copy the data, we want
to pass the requested size to user space in the structure
passed in. The return code in this case is -E2BIG.

Test-Parameters: trivial
Signed-off-by: Olaf Weber <olaf@sgi.com>
Change-Id: I522c11e6ec09bec46121496d526bb258e10295f1
Reviewed-on: https://review.whamcloud.com/25790
Reviewed-by: Amir Shehata <amir.shehata@intel.com>
Tested-by: Amir Shehata <amir.shehata@intel.com>