softap: Show toast msg if SoftAp start failed due to no 5g band support

In DLKM mode DUT 5G capability info can't be fetched on boot up as driver
is not loaded until Wifi/SoftAp turned on at least once. As DUT capability
is not initialized on boot up user can select 5G/Dual band to start hotspot.

This change is to show toast message if the user tries to enables SoftAp
on 5g/Dual band and DUT doesn't support SAP in 5G band.

Change-Id: Iad7064864b066c2d3d5bead673e883ca990bfd99
CRs-fixed: 2484876