[WIFICOND][API] Replace capability BitSet by an int

The capability bit set is standard constrained - 16 bits and no more.
Can use a simpler/lighter int.

Per API council feedback.

Bug: 148680192
Test: atest android.net.wifi
Test: atest com.android.server.wifi
Change-Id: I47e8458d64f998da2e9743ad850687bc56a24cf6