LU-9729 lnet: correct locking in legacy add net

LU-9729 lnet: correct locking in legacy add net

Make sure to unlock the api mutex properly
in lnet_dyn_add_net()

Lustre-change: https://review.whamcloud.com/27907
Lustre-commit: 65326ab2f3e7493f72767cd3c69471f3985c77f6

Test-Parameters: trivial
Signed-off-by: Amir Shehata <amir.shehata@intel.com>
Change-Id: I786545de690ea5966771be3e84d3561b794d55ec
Reviewed-by: Olaf Weber <olaf.weber@hpe.com>
Reviewed-by: Sonia Sharma <sonia.sharma@intel.com>
Signed-off-by: Minh Diep <minh.diep@intel.com>
Reviewed-on: https://review.whamcloud.com/28236
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>