Leak in io.undertow.server.DefaultByteBufferPool on EAP 7.4.16 and 7.4.17

Issue

• After updating to EAP 7.4.16, we have seen leaks until eventual OOMEs and heap dump show buffers accumulating in io.undertow.server.DefaultByteBufferPool$ThreadLocalCache's localsByThread map:

Class Name                                                                                   | Ref. Objects | Shallow Heap | Ref. Shallow Heap | Retained Heap
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[56] class io.undertow.protocols.ssl.UndertowXnioSsl @ 0xaf1b2a10                            |       71,676 |            8 |         1,720,224 |            32
'- DEFAULT_BUFFER_POOL io.undertow.server.DefaultByteBufferPool @ 0xaf1b2a80                 |       71,676 |           64 |         1,720,224 |    20,792,448
   '- threadLocalCache io.undertow.server.DefaultByteBufferPool$ThreadLocalCache @ 0xaf1b2ac0|       71,676 |           16 |         1,720,224 |    18,071,056
      '- localsByThread java.util.HashMap @ 0xaf1b2ad0                                       |       71,676 |           48 |         1,720,224 |    18,071,040
         '- table java.util.HashMap$Node[131072] @ 0xb3c67d20                                |       71,676 |      524,304 |         1,720,224 |    18,070,992
            |- [108494] java.util.HashMap$Node @ 0xb1610fb0                                  |            6 |           32 |               144 |         1,488
            |  |- next java.util.HashMap$Node @ 0xb1def998                                   |            5 |           32 |               120 |         1,240
            |  |- value io.undertow.server.DefaultByteBufferPool$ThreadLocalData @ 0xb15d5e98|            1 |           24 |                24 |           128
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