Clarify securityAlgorithmsUpdated and add new null enums

Per vendor feedback, adds SRTP_NULL, IMS_NULL, clarifies VoWiFi are reserved
for future use, and when state for securityAlgorithmsUpdated is expected to
be cleared.

Bug: b/318426372, b/318425921, b/318426377, b/318427053
Test: m
Change-Id: I465e97a445d330088fb58d2ccc9481cfe360fc07