Allow NetworkAgent "immutable updates" to NetworkCapabilities

This patch loosens the validation checks when a NetworkAgent updates it
NetworkCapabilities: instead of checking that capabilities labeled as
"immutable" stay identical across updates, it is now accepted to change
immutable capabilities in a way that the new NetworkCapabilities
satisfies the old NetworkCapabilities.

This allows a NetworkAgent to update itself in order to match more
requests, but will still catch NetworkAgents that sends degradation
updates causing potentially requests to not match anymore.

Bug: 64125969
Test: runtest frameworks-net
Merged-In: I2a1b3f9c0be6415e40edc989d0c1b03b5631f7b1
Merged-In: I0ab76de59e87c46a6961229399ff7200bce49838
Merged-In: Ied592bf6112574399a1e808da337004e1c35f244
Merged-In: I01e287b4df82a53a522566d33b3166f7801badca
Merged-In: I7ee60daa9c4266e9b9179032815dd7267e06377f
Merged-In: I31ef741eb83d64c476e5930d5762514b5d4cb16f

(cherry picked from commit bae105a5)

Change-Id: I9d630d63336f4db69f3eb52faa8483f1b1e35d16