all: add extra information to serialized endpoints

magicsock.Conn.ParseEndpoint requires a peer's public key,
disco key, and legacy ip/ports in order to do its job.
We currently accomplish that by:

* adding the public key in our wireguard-go fork
* encoding the disco key as magic hostname
* using a bespoke comma-separated encoding

It's a bit messy.

Instead, switch to something simpler: use a json-encoded struct
containing exactly the information we need, in the form we use it.

Our wireguard-go fork still adds the public key to the
address when it passes it to ParseEndpoint, but now the code
compensating for that is just a couple of simple, well-commented lines.
Once this commit is in, we can remove that part of the fork
and remove the compensating code.

Signed-off-by: Josh Bleecher Snyder <josharian@gmail.com>

wgengine/wgcfg/parser_test.go

@@ -53,21 +53,3 @@ func TestParseEndpoint(t *testing.T) {
 		t.Error("Error was expected")
 	}
 }
-
-func TestValidateEndpoints(t *testing.T) {
-	tests := []struct {
-		in   string
-		want error
-	}{
-		{"", nil},
-		{"1.2.3.4:5", nil},
-		{"1.2.3.4:5,6.7.8.9:10", nil},
-		{",", &ParseError{why: "Missing port from endpoint", offender: ""}},
-	}
-	for _, tt := range tests {
-		got := validateEndpoints(tt.in)
-		if !reflect.DeepEqual(got, tt.want) {
-			t.Errorf("%q = %#v (%s); want %#v (%s)", tt.in, got, got, tt.want, tt.want)
-		}
-	}
-}