[22841] Improve `max_allocations` calculation on SHM transport #1770

Job	Run time
sanitizers-ci / asan_fastdds_build	6m 57s
sanitizers-ci / tsan_fastdds_test	4h 3m 35s
sanitizers-ci / asan_discovery_server_test	6m 17s
sanitizers-ci / asan_fastdds_test	4h 58m 52s
	9h 15m 41s

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