LU-9909 lnet: fix memory leak and lnet_interfaces_max

LU-9909 lnet: fix memory leak and lnet_interfaces_max

Free buffer allocated for discover command.

Set lnet_interfaces_max to LNET_INTERFACES_MAX_DEFAULT if
it's not defined or if it's being set to something below
LNET_INTERFACES_MIN.

For lnet_ping() and lnet_discover() if the provided space
can fit more NIDs than lnet_interfaces_max then ensure only
lnet_interfaces_max is copied into the buffer.

Test-Parameters: trivial
Signed-off-by: Amir Shehata <amir.shehata@intel.com>
Change-Id: I19aed712f40a8bf44d2fb112588e9ae07257469f
Reviewed-on: https://review.whamcloud.com/28702
Tested-by: Jenkins
Reviewed-by: Sonia Sharma <sonia.sharma@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Olaf Weber <olaf.weber@hpe.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>