Updates documentation mentioning all IP interfaces are available.

As of https://r.android.com/1242747, IPv6-only interfaces are also
available through NetworkInterface to non-system apps. This change
updates the documentation to reflect that.

Bug: 141455849
Test: atest NetworkInterfaceTest
Change-Id: Ib2420256ba115830f34e37e5ce1bc8a5f6e13bef
(cherry picked from aosp/1242748)
1 file changed