RFR: 8276845: (fs) java/nio/file/spi/SetDefaultProvider.java fails on x86_32

[Aleksey Shipilev]

x86_32 takes a path that requires `newFileChannel` implemented in `TestProvider`. Otherwise the test fails with the exception. The implementation is the same as for `newByteChannel`.

Additional testing:
 - [x] Linux x86_32 fastdebug, test now passes
 - [x] Linux x86_64 fastdebug, test still passes

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

Commit messages:
 - Fix

Changes: https://git.openjdk.java.net/jdk/pull/6307/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6307&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8276845
  Stats: 11 lines in 1 file changed: 11 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6307.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6307/head:pull/6307

PR: https://git.openjdk.java.net/jdk/pull/6307