[API] Soft AP multiple/bridge javadoc update

Clarify that Soft APs may have multiple instances - which are always
bridged. I.e. the combination of all instances act as a single Soft AP
from the perspective of the caller (the defintion of bridging).

Bug: 181891841
Test: make docs
Change-Id: I05ee2beaae6ab2d58e8e5db7c5e4bf98cd5dfa22
1 file changed