RFR: 8374802: Assert if UDP receive buffer is too small to hold capacity to avoid hanging test

[Andreas Steiner]

To avoid the test is hanging due to the too small receive buffer, check the receive buffer can hold the capacity. If not, assert.

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Commit messages:
 - 8374802: Assert if UDP receive buffer is too small to hold capacity to avoid hanging test

Changes: https://git.openjdk.org/jdk/pull/29251/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29251&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8374802
  Stats: 6 lines in 1 file changed: 6 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/29251.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29251/head:pull/29251

PR: https://git.openjdk.org/jdk/pull/29251