Audit of node referencing:

Audit of node referencing:
 * Enhance readability of some functions WRT node referencing by putting blocks around areas where node references are held
 * Various bits of consistency of the usage of node references; always unreference them at the point at which they are no longer used. Don't reuse variables implicitly.
 * Significant overhaul of the usage of bf_node and ieee80211_cb.ni. Always hold a reference with aforementioned variable and always unreference it properly.

git-svn-id: http://madwifi-project.org/svn/madwifi/trunk@2839 0192ed92-7a03-0410-a25b-9323aeb14dbd