samples: bpf: Update outdated error message

Currently, under samples, several methods are being used to load bpf
program.

Since using libbpf is preferred solution, lots of previously used
'load_bpf_file' from bpf_load are replaced with 'bpf_prog_load_xattr'
from libbpf.

But some of the error messages still show up as 'load_bpf_file' instead
of 'bpf_prog_load_xattr'.

This commit fixes outdated errror messages under samples and fixes some
code style issues.

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20191107005153.31541-2-danieltimlee@gmail.com
diff --git a/samples/bpf/xdp1_user.c b/samples/bpf/xdp1_user.c
index a8e5fa0..3e553ee 100644
--- a/samples/bpf/xdp1_user.c
+++ b/samples/bpf/xdp1_user.c
@@ -139,7 +139,7 @@ int main(int argc, char **argv)
 	map_fd = bpf_map__fd(map);
 
 	if (!prog_fd) {
-		printf("load_bpf_file: %s\n", strerror(errno));
+		printf("bpf_prog_load_xattr: %s\n", strerror(errno));
 		return 1;
 	}