bpf: Update iterators.lskel-big-endian.h

The last iterators update (commit 515ee52 ("bpf: make preloaded
map iterators to display map elements count")) missed the big-endian
skeleton. Update it by running "make big" with Debian clang version
21.0.0 (++20250706105601+01c97b4953e8-1~exp1~20250706225612.1558).

Signed-off-by: Ilya Leoshkevich <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: iii-i