LU-11763 lnet: Change "lctl network configure" to always take net device info

LU-11763 lnet: Change "lctl network configure" to always take net device info

Currently, if the network interface is not specified
in the lustre.conf file, then the "lctl network configure"
command configures network at LND level using default
interface values for socklnd and o2iblnd.

With this patch, lnet_get_networks() is modified such
that if the network device info is not provided, then
it will get the first available network interface,
say "intf" and pass "tcp(intf)" to lnet_parse_networks().
If no network device is found, then it will pass NULL.

Test-Parameters: trivial
Change-Id: I3e3d8fac5f9837330d8787f36826ef9b2b4ea93e
Signed-off-by: Sonia Sharma <sharmaso@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/34764
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Amir Shehata <ashehata@whamcloud.com>