Limit unprivileged keepalives per uid

Public APIs for creating unprivileged NATT socket keepalive
might allow users to exhaust resource if malicious apps try
to create keepalives with fd which is not created by
IpSecService through binder call. Thus, this change add
customizable limitation per uid to prevent resource exhaustion
attack.

Bug: 129371366
Bug: 132307230
Test: atest FrameworksNetTests

Clean cherry-pick of aosp/954040
Merged-In: Ibcb91105e46f7e898b8aa7c2babc3344ef2c6257
Merged-In: Ia667386c1a8949839871a6949d79552d9c8b88f0

Change-Id: I92f6d977b6dfde4e1bf74df6b60c9a0b9e8eec40