iwlagn: rename iwlagn_set_dynamic_key

We now have iwlagn_set_dynamic_key() and
iwl_set_dynamic_key() which is confusing,
rename the former to iwlagn_send_sta_key()
to better reflect what it does -- it only
sends a command and doesn't change driver
state.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>