tools: bpftool: fix format string for p_err() in query_flow_dissector()

The format string passed to one call to the p_err() function in
query_flow_dissector() does not match the value that should be printed,
resulting in some garbage integer being printed instead of
strerror(errno) if /proc/self/ns/net cannot be open. Let's fix the
format string.

Fixes: 7f0c57f ("bpftool: show flow_dissector attachment status")
Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/bpf/bpftool/net.c

@@ -226,7 +226,7 @@ static int query_flow_dissector(struct bpf_attach_info *attach_info)
 
 	fd = open("/proc/self/ns/net", O_RDONLY);
 	if (fd < 0) {
-		p_err("can't open /proc/self/ns/net: %d",
+		p_err("can't open /proc/self/ns/net: %s",
 		      strerror(errno));
 		return -1;
 	}