pods in nat-outgoing shoul dnot SNAT to local host

When a pod is accessing a local host, it should not get SNATed as the
host when it is in a nat-outgoing ippool. (a) it is unnecessary as the
local node can be accessed and (b) there is no way to return the traffic
as is it would return to the host itself.

refs projectcalico#7252

felix/bpf-gpl/tc.c

@@ -445,7 +445,12 @@ static CALI_BPF_INLINE void calico_tc_process_ct_lookup(struct cali_tc_ctx *ctx)
 
 		// Check whether the workload needs outgoing NAT to this address.
 		if (r->flags & CALI_RT_NAT_OUT) {
-			if (!(cali_rt_lookup_flags(&ctx->state->post_nat_ip_dst) & CALI_RT_IN_POOL)) {
+			struct cali_rt *rt = cali_rt_lookup(&ctx->state->post_nat_ip_dst);
+			enum cali_rt_flags flags = CALI_RT_UNKNOWN;
+			if (rt) {
+				flags = rt->flags;
+			}
+			if (!(flags & CALI_RT_IN_POOL) && !cali_rt_flags_local_host(flags)) {
 				CALI_DEBUG("Source is in NAT-outgoing pool "
 					   "but dest is not, need to SNAT.\n");
 				ctx->state->flags |= CALI_ST_NAT_OUTGOING;

felix/fv/bpf_test.go

@@ -1335,6 +1335,7 @@ func describeBPFTests(opts ...bpfTestOpt) bool {
 					It("should handle NAT outgoing", func() {
 						By("SNATting outgoing traffic with the flag set")
 						cc.ExpectSNAT(w[0][0], felixIP(0), hostW[1])
+						cc.Expect(Some, w[0][0], hostW[0]) // no snat
 						cc.CheckConnectivity(conntrackChecks(tc.Felixes)...)
 
 						if testOpts.tunnel == "none" {