Fix stale CASE exchange blocking new session handshake #2380

Job	Run time
build_and_test (mbedtls)	6m 13s
build_and_test (mbedtls, alloc)	6m 2s
build_and_test (rustcrypto)	7m 7s
build_and_test (rustcrypto, os)	16m 13s
build_and_test (openssl)	5m 36s
build_and_test (openssl, alloc)	5m 29s
build_and_test (mbedtls, os)	8m 26s
build_and_test (rustcrypto, alloc)	5m 29s
build_and_test (openssl, os)	7m 43s
	1h 8m 18s

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