net80211: ieee80211_dump_node() cosmetics

Printing %p does not need the 0x prefix and while here mark the
ieee80211_node_table argument unused given we do not need it in the
current incarnation of the function.

Sponsored by: The FreeBSD Foundation

(cherry picked from commit c3db9d4a1439e0144415e007599a94dde4bee01b)