Fix some errors and move the ir_capabilities to irn_capabilities in per node rc state. (r255966, r255969, 255970)
* some minor errors fixed.
* add struct ieee80211_ratectl_node. this is the common state that all per node rc
  state, i.e. ieee80211_[amrr|sample]_node, should contains it as the first field.
* move ir_capabilities to irn_capabilities in ieee80211_ratectl_node. ieee80211_ratectl
  is readonly, so ir_capabilities can't be set. And, the capabilities is not a part of
  rc algo. It seems that it should be put in the per node rc state. Interface of
  ieee80211_ratectl_node_init() and its callers are updated. References to ir_capabilities
  are also adapted.
* fix the error refering rateCode of ieee80211_rate_table.
* add ieee80211_ratectl_[node_is11n|get_rateset] to the ratectl api.
  rc algos all need these functions.
* change the naming conversion of IEEE80211_RATECTL_FLAG_*.