LU-9480 lnet: add lnet_interfaces_max tunable

LU-9480 lnet: add lnet_interfaces_max tunable

Add an lnet_interfaces_max tunable value, that describes the maximum
number of interfaces per node. This tunable is primarily useful for
sanity checks prior to allocating memory.

Allow lnet_interfaces_max to be set and get from the sysfs interface.

Add LNET_INTERFACES_MIN, value 16, as the minimum value.

Add LNET_INTERFACES_MAX_DEFAULT, value 200, as the default value. This
value was chosen to ensure that the size of an LNet ping message with
any associated LND overhead would fit in 4096 bytes.

(The LNET_INTERFACES_MAX name was not reused to allow for the early
detection of issues when merging code that uses it.)

Rename LNET_NUM_INTERFACES to LNET_INTERFACES_NUM

Test-Parameters: trivial
Signed-off-by: Olaf Weber <olaf@sgi.com>
Signed-off-by: Amir Shehata <amir.shehata@intel.com>
Change-Id: I9bdc72cc688a414f7658fed93f84c9885c8342be
Reviewed-on: https://review.whamcloud.com/25770