Address API council feedback on RateStats API

1. Changed the values of WIFI_SPATIAL_STREAMS_ constants to start from
the value of one.
2. In the javadoc described the ordering of RateStats for
getRateStats().

Bug: 183656332

Test: atest android.net.wifi

Signed-off-by: Mingguang Xu <mingguangxu@google.com>
Change-Id: Ib886bf698c0e7e140a60c16d9ab07b759a7209e9
2 files changed