wifi(implementation): Use strlen for size of ssid

Looks like the legacy hal uses a null termination for indicating the
size of ssid.

While there,
Use the helper function to convert wifi band from hidl to legacy.

Bug: 35765841
Test: Integration tests pass now.
Change-Id: Ie480f9d6735a21c5ccedfc68bfde5f0d920dcdc9
1 file changed