Ignore basic MCS set information found in association responses.

Ignore basic MCS set information found in association responses.

Some APs (Aruba 105) send a bogus basic MCS set in assoc responses
which prevents us from enabling 11n support with those APs, while
these APs still behave as if were were an 11n client which renders
the association unusable.

The basic MSC set is already provided in beacons anyway, and the
802.11 2012 standard says the basic MSC set is reserved in frames
other than beacons (see Table 8-130).

ok mpi@