[DO NOT MERGE] passpoint: validate decorated identity prefix

Bug: 246539931
Test: atest FrameworksWifiTests
      insatll PoC to verify the issue does not happen
Change-Id: I59144c43d2ee9590c8d973e24877e56aaf395b33
(cherry picked from commit df9d477011d9e64857dea3658cba1fc25e5d18cc)
1 file changed
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