internal/clientinfo: ignoring localhost entry for hostsfile mapping

Otherwise, actual hostname will be overriden with "localhost", which is
rather confusing/bad for UX.

internal/clientinfo/hostsfile_test.go

@@ -0,0 +1,33 @@
+package clientinfo
+
+import (
+	"testing"
+)
+
+func Test_hostsFile_LookupHostnameByIP(t *testing.T) {
+	tests := []struct {
+		name             string
+		ip               string
+		hostnames        []string
+		expectedHostname string
+	}{
+		{"ipv4 loopback", "127.0.0.1", []string{ipv4LocalhostName}, ""},
+		{"ipv6 loopback", "::1", []string{ipv6LocalhostName, ipv6LoopbackName}, ""},
+		{"non-localhost", "::1", []string{"foo"}, "foo"},
+		{"multiple hostnames", "::1", []string{ipv4LocalhostName, "foo"}, "foo"},
+	}
+
+	for _, tc := range tests {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			hf := &hostsFile{m: make(map[string][]string)}
+			hf.mu.Lock()
+			hf.m[tc.ip] = tc.hostnames
+			hf.mu.Unlock()
+			if got := hf.LookupHostnameByIP(tc.ip); got != tc.expectedHostname {
+				t.Errorf("unpexpected result, want: %q, got: %q", tc.expectedHostname, got)
+			}
+		})
+	}
+}