[11u] RFR: 8236464: SO_LINGER option is ignored by SSLSocket in JDK 11

[Lindenmaier, Goetz]

Hi, 

I am downporting this for parity with 11.0.9-oracle.
I had to do quite some adaptions:
http://cr.openjdk.java.net/~goetz/wr20/8236464-SSLSocket_LINGER-jdk11/01/

src/java.base/share/classes/sun/security/ssl/SSLSocketImpl.java
The change renames a method that is not there in 11. 
I skipped the renaming and applied the functional change
that is in the same chunk.

src/java.base/share/classes/sun/security/ssl/TransportContext.java
The code deleted differs, because in 15 explicit locking 
is used. I added a synchronized block in the method 
introduced.

Please review.

https://bugs.openjdk.java.net/browse/JDK-8236464
https://hg.openjdk.java.net/jdk/jdk/rev/c783b60f48db

Best regards,
  Goetz