NetworkCapabilities: fix describeImmutableDifferences

This patch fixes the mask used in describeImmutableDifferences which did
not correctly turn NET_CAPABILITY_NOT_METERED into bit flag.

Bug: 63326103
Test: added unit tests, runtest frameworks-net
Merged-In: Ib6b390b1daef5912859302692af7dcd6cfd3e39a
Merged-In: If38efacdeec8476880835657938e435f9b598525
Merged-In: Ieccad46fcffcaf748f5644b04617e9a82527000e
Merged-In: I533ef8fe369cec19d283ff2950314fce6e28cffd
Merged-In: I12636c6699ff60487a28570208e819ea0b66fa2e
Merged-In: Ie5df14e0ea1c12e0cfabe87978ac6c9b744353b2

(cherry picked from commit 2ecb9408)

Change-Id: I74ecf34a2c079c74152d00caea2c220e9c6d1fa5