bpf: fix _htons occurences in test_progs

Dave reported that on sparc test_progs generates buggy swapped
eth->h_proto protocol comparisons:

  10: (15) if r3 == 0xdd86 goto pc+9
   R0=imm2,min_value=2,max_value=2 R1=pkt(id=0,off=0,r=14) R2=pkt_end R3=inv
   R4=pkt(id=0,off=14,r=14) R5=inv56 R10=fp

This is due to the unconditional ...

  #define htons __builtin_bswap16
  #define ntohs __builtin_bswap16

... in test_progs that causes this. Make use of asm/byteorder.h
and use __constant_htons() where possible and only perform the
bswap16 when on little endian in non-constant case.

Fixes: 6882804c916b ("selftests/bpf: add a test for overlapping packet range checks")
Fixes: 37821613626e ("selftests/bpf: add l4 load balancer test based on sched_cls")
Reported-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/tools/testing/selftests/bpf/test_progs.c b/tools/testing/selftests/bpf/test_progs.c
index 5275d4a..7c2d899 100644
--- a/tools/testing/selftests/bpf/test_progs.c
+++ b/tools/testing/selftests/bpf/test_progs.c
@@ -30,8 +30,6 @@ typedef __u16 __sum16;
 #include "test_iptunnel_common.h"
 #include "bpf_util.h"
 
-#define _htons __builtin_bswap16
-
 static int error_cnt, pass_cnt;
 
 #define MAGIC_BYTES 123
@@ -42,10 +40,10 @@ static struct {
 	struct iphdr iph;
 	struct tcphdr tcp;
 } __packed pkt_v4 = {
-	.eth.h_proto = _htons(ETH_P_IP),
+	.eth.h_proto = bpf_htons(ETH_P_IP),
 	.iph.ihl = 5,
 	.iph.protocol = 6,
-	.iph.tot_len = _htons(MAGIC_BYTES),
+	.iph.tot_len = bpf_htons(MAGIC_BYTES),
 	.tcp.urg_ptr = 123,
 };
 
@@ -55,9 +53,9 @@ static struct {
 	struct ipv6hdr iph;
 	struct tcphdr tcp;
 } __packed pkt_v6 = {
-	.eth.h_proto = _htons(ETH_P_IPV6),
+	.eth.h_proto = bpf_htons(ETH_P_IPV6),
 	.iph.nexthdr = 6,
-	.iph.payload_len = _htons(MAGIC_BYTES),
+	.iph.payload_len = bpf_htons(MAGIC_BYTES),
 	.tcp.urg_ptr = 123,
 };