Bump big value size in AsyncMcClient tests
Bump big value size in AsyncMcClient tests

Summary: Title.

Test Plan:
Check that AsyncMcClient reconnect* tests pass.  Also, stress running `reconnectAscii` passes:

    fbmake runtests reconnectAscii --stress-runs 100 --stress-run-only-pass

Reviewed By: spalamarchuk

Differential Revision: D2899415

fb-gh-sync-id: cbf2a2c04ec9fef65e1434abff77cbdd656afc52

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