routerrpc: modify field orders based on their assigned number

This commit is a pure refactoring which sorts the fields in
`SendPaymentRequest` so it's easier to see what number to use when
adding a new field.

lnrpc/routerrpc/router.proto

@@ -164,13 +164,6 @@ message SendPaymentRequest {
     */
     int64 amt = 2;
 
-    /*
-    Number of millisatoshis to send.
-
-    The fields amt and amt_msat are mutually exclusive.
-    */
-    int64 amt_msat = 12;
-
     // The hash to use within the payment's HTLC
     bytes payment_hash = 3;
 
@@ -180,9 +173,6 @@ message SendPaymentRequest {
     */
     int32 final_cltv_delta = 4;
 
-    // An optional payment addr to be included within the last hop of the route.
-    bytes payment_addr = 20;
-
     /*
     A bare-bones invoice for a payment within the Lightning Network.  With the
     details of the invoice, the sender has all the data necessary to send a
@@ -210,17 +200,6 @@ message SendPaymentRequest {
     */
     int64 fee_limit_sat = 7;
 
-    /*
-    The maximum number of millisatoshis that will be paid as a fee of the
-    payment. If this field is left to the default value of 0, only zero-fee
-    routes will be considered. This usually means single hop routes connecting
-    directly to the destination. To send the payment without a fee limit, use
-    max int here.
-
-    The fields fee_limit_sat and fee_limit_msat are mutually exclusive.
-    */
-    int64 fee_limit_msat = 13;
-
     /*
     Deprecated, use outgoing_chan_ids. The channel id of the channel that must
     be taken to the first hop. If zero, any channel may be used (unless
@@ -229,19 +208,8 @@ message SendPaymentRequest {
     uint64 outgoing_chan_id = 8 [jstype = JS_STRING, deprecated = true];
 
     /*
-    The channel ids of the channels are allowed for the first hop. If empty,
-    any channel may be used.
-    */
-    repeated uint64 outgoing_chan_ids = 19;
-
-    /*
-    The pubkey of the last hop of the route. If empty, any hop may be used.
-    */
-    bytes last_hop_pubkey = 14;
-
-    /*
-    An optional maximum total time lock for the route. This should not exceed
-    lnd's `--max-cltv-expiry` setting. If zero, then the value of
+    An optional maximum total time lock for the route. This should not
+    exceed lnd's `--max-cltv-expiry` setting. If zero, then the value of
     `--max-cltv-expiry` is enforced.
     */
     int32 cltv_limit = 9;
@@ -260,6 +228,29 @@ message SendPaymentRequest {
     */
     map<uint64, bytes> dest_custom_records = 11;
 
+    /*
+    Number of millisatoshis to send.
+
+    The fields amt and amt_msat are mutually exclusive.
+    */
+    int64 amt_msat = 12;
+
+    /*
+    The maximum number of millisatoshis that will be paid as a fee of the
+    payment. If this field is left to the default value of 0, only zero-fee
+    routes will be considered. This usually means single hop routes connecting
+    directly to the destination. To send the payment without a fee limit, use
+    max int here.
+
+    The fields fee_limit_sat and fee_limit_msat are mutually exclusive.
+    */
+    int64 fee_limit_msat = 13;
+
+    /*
+    The pubkey of the last hop of the route. If empty, any hop may be used.
+    */
+    bytes last_hop_pubkey = 14;
+
     // If set, circular payments to self are permitted.
     bool allow_self_payment = 15;
 
@@ -284,6 +275,15 @@ message SendPaymentRequest {
     */
     bool no_inflight_updates = 18;
 
+    /*
+    The channel ids of the channels are allowed for the first hop. If empty,
+    any channel may be used.
+    */
+    repeated uint64 outgoing_chan_ids = 19;
+
+    // An optional payment addr to be included within the last hop of the route.
+    bytes payment_addr = 20;
+
     /*
     The largest payment split that should be attempted when making a payment if
     splitting is necessary. Setting this value will effectively cause lnd to