mesh: Do not enable HE on 5 GHz without VHT

mesh: Do not enable HE on 5 GHz without VHT

The commit ad9a1bfe788e ("nl80211: Share VHT channel configuration for
HE") always enforced that VHT is enabled when HE was enabled. This broke
the mesh functionality on 2.4 GHz with HE because ibss_mesh_setup_freq()
isn't setting up the VHT parameters for 2.4 GHz.

This problem was resolved for 2.4 GHz by commit df4f959988b6 ("nl80211:
Don't force VHT channel definition with HE"), but it is still possible
to disable VHT during the mesh/IBSS freq setup on 5 GHz - which would
result in the same problem as seen on 2.4 GHz.

The code enabling HE for IBSS/mesh must now make sure that it doesn't
enable HE when VHT could be enforced by the nl80211 driver code but
disabled by the user.

Fixes: 3459c54ac78b ("mesh: Add support for HE mode")
Signed-off-by: Sven Eckelmann <seckelmann@datto.com>