Adjust Tag availability checking mechanism

1. The nonce could only set by NfcService
2. Use random number instead of the system time
3. Clear the nonce after disconnecting to the tag

Bug: 199291025
Test: test with some reader apps, test pass
Change-Id: Idfce8dfe75282d10b00fab68dda8c9a8629757a3
Merged-In: Idfce8dfe75282d10b00fab68dda8c9a8629757a3
1 file changed