bpftool, musl compat: Replace sys/fcntl.h by fcntl.h

musl does not like including sys/fcntl.h directly:

    [...]
    1 | #warning redirecting incorrect #include <sys/fcntl.h> to <fcntl.h>
    [...]

Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/20220424051022.2619648-5-asmadeus@codewreck.org