use-of-uninitialized-value in ofpbuf prealloc tailroom

use-of-uninitialized-value in ofpbuf prealloc tailroom: a task in MiMo-V2.6-RL-oss: Agentic RL Environments (MiMo RL release). MemorySanitizer: use-of-uninitialized-value in function ofpbuf prealloc tailroom in file openvswitch/lib/ofpbuf.c