The "find node" function call will increase the node reference anyway;
so there's no reason to hold the node table lock during the MLME change.
The only reason I could think of is to stop overlapping mlme ioctls
from causing issues, but this should be fixed a different way.
This fixes a whole class of LORs that creep up when nodes are being
timed out or removed by hostapd.
Tested:
* AR5416, hostap, with nodes coming and going. No LORs or stability
issues were observed.