cmp_server.c: adapt server for kem #899

Job	Run time
compiler (gcc-7, ubuntu-20.04)	6m 43s
compiler (gcc-8, ubuntu-20.04)	9m 17s
compiler (gcc-9, ubuntu-20.04)	7m 35s
compiler (gcc-10, ubuntu-20.04)	8m 11s
compiler (gcc-11, ubuntu-22.04)	8m 0s
compiler (gcc-12, ubuntu-22.04)	11m 14s
compiler (gcc-13, ubuntu-22.04, ubuntu-toolchain-r/test)	8m 42s
compiler (clang-6.0, ubuntu-20.04)	2m 36s
compiler (clang-7, ubuntu-20.04)	7m 57s
compiler (clang-8, ubuntu-20.04)	3m 41s
compiler (clang-9, ubuntu-20.04)	8m 29s
compiler (clang-10, ubuntu-20.04)	7m 50s
compiler (clang-11, ubuntu-20.04)	7m 0s
compiler (clang-12, ubuntu-20.04)	6m 10s
compiler (clang-13, ubuntu-22.04)	9m 3s
compiler (clang-14, ubuntu-22.04)	6m 39s
compiler (clang-15, ubuntu-22.04, jammy)	8m 6s
compiler (clang-16, ubuntu-22.04, jammy)	6m 45s
	2h 13m 58s

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