[$] Hash table memory usage and a BPF interpreter bug

Anton Protopopov led a short discussion at the 2025 Linux Storage, Filesystem,
Memory-Management, and BPF Summit about amount of memory used
by hash tables in BPF programs. He thinks that the current memory layout is
inefficient, and wants to split the structure that holds table entries into two
variants for different kinds of maps. When that proposal proved
uncontroversial, he also took the chance to talk about a bug in BPF's call
instruction.