Fix `FD_RUNTIME_MIN_STAKE_INSN_CUS`

[mmcgee-jump]

/* The stake program is now a BPF program which means that there is a
   variable cost in CUs to execute the stake program.  This is the
   absolute minimum cost of executing the stake program.

   FIXME: This is a reasonable estimate based off of BPF withdraw
   instructions.  The hard bound still needs to be determined. */

#define FD_RUNTIME_MIN_STAKE_INSN_CUS (6000UL)