qcacld-3.0: Make net_dev_hold_ref_count as atomic

Currently the reference count variable used to detect the net device
reference leaks is not atomic. Because of this, the reference count
updation may not be reliable in multi thread scenario.

To address this, make the net_dev_hold_ref_count increment and
decrement as atomic.

Change-Id: Ifa87177164e87880d0c6d71fb40ca03a3919519e
CRs-Fixed: 2868029