wifi: Gscan struct conversion changes

Rename |Scan| to |Gscan| because that is the naming we've been using in
WifiLegacyHal.
Also group all the gscan related sturct conversion methods.

Bug: 31991459
Test: Compiles
Change-Id: Ie64bcc032a0058b5b20d0bb701020cdf7bf08890
2 files changed