Record netd_stable_secret_prop in compat infra.

Commit: abb1ba65 added policy for a
new property, which was not present in O.  This policy introduced a
new type.  Record it as such.

Bug: 62573845
Test: None, prebuilt change only.
Change-Id: I7d90cd69a5e6e29677598cc109676d5b1ce5ba05