iwinfo: Return the hw and ht modes supported the by the WiFi-chipset.

In order for LuCI to work correctly we need to provide the ht and hw modes that is supported by the WiFI-chipset and not the currently used modes. This implementation borrows from iwinfo_wl.c regarding how to use the hw modes to set the ht modes.

A known limitation is that there might exist chipsets which are 160 MHz capable in 802.11ax mode and not in 802.11ac mode, which will result in an invalid bandwidth representation.