Add an UNKNOWN_UID constant to WifiConfiguration.

This value will be used to indicate that one of the various UIDs
tracked stored in the WifiConfiguration is unknown. Currently the
code just uses "-1" everywhere for this purpose; a constant is
clearer.

Bug: 20081183
Change-Id: Id865da9284f642587eed11f67685e5b12ce772c2
1 file changed