mesh: Clear wpa_s cipher selection on starting mesh

mesh: Clear wpa_s cipher selection on starting mesh

This is needed to avoid hitting WEP/TKIP detection in
ibss_mesh_setup_freq() if the previous connection used WEP or TKIP.
Previously, that could have resulted in VHT and HT getting disabled for
the mesh connection.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>