RFR: 8333772: Incorrect Kerberos behavior when udp_preference_limit = 0

[Weijun Wang]

Allow `udp_preference_limit = 0` to force TCP.

The reason for this bug is that it was read in a similar way as `kdc_timeout` and `max_retries`, both must be positive to have effect.

-------------

Commit messages:
 - the fix

Changes: https://git.openjdk.org/jdk/pull/19638/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19638&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8333772
  Stats: 220 lines in 4 files changed: 188 ins; 9 del; 23 mod
  Patch: https://git.openjdk.org/jdk/pull/19638.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19638/head:pull/19638

PR: https://git.openjdk.org/jdk/pull/19638