RFR: 8290005: com/sun/jndi/ldap/LdapCBPropertiesTest.java failling with NullPointerException

[Matthew Donovan]

In this PR, I added methods to the TransportContext class to synchronize access to the handshakeContext field. I also updated locations in the code that rely on the handshakeContext field to not be null to use the synchronized methods.

Thanks

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Commit messages:
 - 8290005: com/sun/jndi/ldap/LdapCBPropertiesTest.java failling with NullPointerException

Changes: https://git.openjdk.org/jdk/pull/13742/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13742&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8290005
  Stats: 82 lines in 3 files changed: 51 ins; 20 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/13742.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13742/head:pull/13742

PR: https://git.openjdk.org/jdk/pull/13742