Contrary to the IEEE specification, some access points apparently
set the Spectrum Mgmt bit in the capabilities field even when
broadcasting on a 2.4GHz band that does not require spectrum
management. Allow gPXE to attempt to connect to such networks;
if spectrum management is really required, our advertisement
of capabilities not including it will result in an association
failure.

Reported-by: Peter Meyer <residue@xmail.net>

Signed-off-by: Marty Connor <mdc@etherboot.org>