lwip: increase TCP window somewhat

With a bit increased TCP window, all write requests (max 4k) can be honoured by lwip
in one go, without having lwip to call our callback for us to offer more data.

This may solve a lot of mysterious "data still not sent" errors, when
new data is offered to be sent.

Author: eriksl

lwipopts.h

@@ -1,6 +1,6 @@
 // lwip core
 
-#define MEM_SIZE					(6 * 1024)
+#define MEM_SIZE					(7 * 1024)
 #define MEMP_NUM_PBUF				16
 #define MEMP_NUM_UDP_PCB			8 // do not decrease!
 #define MEMP_NUM_TCP_PCB			4 // do not decrease!
@@ -27,9 +27,9 @@
 #define DHCP_DOES_ARP_CHECK			0
 #define TCP_QUEUE_OOSEQ				1
 #define TCP_MSS						1460
-#define TCP_WND						(2 * TCP_MSS)
+#define TCP_WND						(3 * TCP_MSS)
 #define TCP_SND_BUF					TCP_WND
-#define TCP_SND_QUEUELEN			4
+#define TCP_SND_QUEUELEN			(2 * TCP_SND_BUF / TCP_MSS)
 #define TCP_SNDLOWAT				1
 #define TCP_SNDQUEUELOWAT			(TCP_SND_QUEUELEN - 1)
 #define TCP_OVERSIZE				TCP_MSS

memory-log

@@ -10546,3 +10546,19 @@ Sun Sep 12 19:59:32 CEST 2021 e985629 lwip: a few tweaks in the config
     iram:    available:  32 k, used:  27897, free:   4871, 14 %
     dram:    available:  78 k, used:  68857, free:  11408, 14 %
     irom:    available: 592 k, used: 429128, free: 177080, 29 %
+Sun Sep 12 20:01:38 CEST 2021 52d406a io: get rid of hardcoded period for fast/slow timer periodic timers.
+    iram:    available:  32 k, used:  27897, free:   4871, 14 %
+    dram:    available:  78 k, used:  68857, free:  11408, 14 %
+    irom:    available: 592 k, used: 429160, free: 177048, 29 %
+Mon Sep 13 13:05:02 CEST 2021 52d406a io: get rid of hardcoded period for fast/slow timer periodic timers.
+    iram:    available:  32 k, used:  27897, free:   4871, 14 %
+    dram:    available:  78 k, used:  68857, free:  11408, 14 %
+    irom:    available: 592 k, used: 429208, free: 177000, 29 %
+Mon Sep 13 13:11:56 CEST 2021 52d406a io: get rid of hardcoded period for fast/slow timer periodic timers.
+    iram:    available:  32 k, used:  27897, free:   4871, 14 %
+    dram:    available:  78 k, used:  70425, free:   9840, 12 %
+    irom:    available: 592 k, used: 429208, free: 177000, 29 %
+Mon Sep 13 13:12:44 CEST 2021 52d406a io: get rid of hardcoded period for fast/slow timer periodic timers.
+    iram:    available:  32 k, used:  27897, free:   4871, 14 %
+    dram:    available:  78 k, used:  71449, free:   8816, 10 %
+    irom:    available: 592 k, used: 429208, free: 177000, 29 %