tools, bpf_asm: Hard error on out of range jumps

Per discussion at [0] this was originally introduced as a warning due
to concerns about breaking existing code, but a hard error probably
makes more sense, especially given that concerns about breakage were
only speculation.

  [0] https://lore.kernel.org/bpf/c964892195a6b91d20a67691448567ef528ffa6d.camel@linux.ibm.com/T/#tSigned-off-by: NIan Denhardt <ian@zenhack.net>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NIlya Leoshkevich <iii@linux.ibm.com>
Link: https://lore.kernel.org/bpf/a6b6c7516f5d559049d669968e953b4a8d7adea3.1614201868.git.ian@zenhack.net

tools/bpf/bpf_exp.y

@@ -549,9 +549,11 @@ static uint8_t bpf_encode_jt_jf_offset(int off, int i)
 {
 	int delta = off - i - 1;
 
-	if (delta < 0 || delta > 255)
-		fprintf(stderr, "warning: insn #%d jumps to insn #%d, "
+	if (delta < 0 || delta > 255) {
+		fprintf(stderr, "error: insn #%d jumps to insn #%d, "
 				"which is out of range\n", i, off);
+		exit(1);
+	}
 	return (uint8_t) delta;
 }