RFR: 8163921: HttpURLConnection default Accept header is malformed according to HTTP/1.1 RFC

[Daniel Jeliński]

Fix RFC compliance.
Tier1 and tier2 passed.

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Commit messages:
 - Fix default Accept header

Changes: https://git.openjdk.java.net/jdk/pull/7181/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7181&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8163921
  Stats: 7 lines in 2 files changed: 0 ins; 0 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7181.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7181/head:pull/7181

PR: https://git.openjdk.java.net/jdk/pull/7181