wifi: Add Iface related method implementations in WifiChip

Add the iface creation/retrieval/list method implementations in WifiChip.
WifiChip does not yet support the chip mode configuration. So, all
|createIface| method calls succeed today. Once the mode configuration
changes are in place, we will deny iface creation requests depending on
the iface combination supported in the current mode.

The iface objects are all invalidated and deleted on mode switches and
when HAL is stopped.

While there,
Change the |callbacks_| member to std::vector instead of std::set. We
don't really need a set to store the list of callbacks.

Bug: 31943042
Test: Compiles
Change-Id: Ic94864c8b11aabbe569b5157d68d6056364a3c4c