Increase LWIP timeouts to avoid MDNS panics (#2653)

Bump up the LWIP_ARP setting to increase the LWIP timeout pool to
avoid a panic when using SimpleMDNS and TCP clients.

Fixes #2650

Author: earlephilhower

include/lwipopts.h

@@ -30,7 +30,7 @@ extern unsigned long __lwip_rand(void);
 #define MEMP_NUM_TCP_SEG              (32)
 #define MEMP_NUM_ARP_QUEUE            (10)
 #define PBUF_POOL_SIZE                (__LWIP_MEMMULT > 1 ? 32 : 24)
-#define LWIP_ARP                      5
+#define LWIP_ARP                      7
 #define LWIP_ETHERNET                 1
 #define LWIP_ICMP                     1
 #define LWIP_RAW                      1