mac80211: Do not send mesh HWMP PREQ if HWMP is disabled

When trying to transmit to an unknown destination, the mesh code would
unconditionally transmit a HWMP PREQ even if HWMP is not the current
path selection algorithm.

Signed-off-by: Nicolas Cavallari <nicolas.cavallari@green-communications.fr>
Link: https://lore.kernel.org/r/20200305140409.12204-1-cavallar@lri.fr


Signed-off-by: Johannes Berg <johannes.berg@intel.com>