lwIP | stm32h7: Add Ethernet driver for STM32H743ZI Nucleo (!37)

[Claudio Grasso (@ClaudioGrasso)]

Claudio Grasso commented on a discussion on stm32h7/include/lwipbspopts.h: https://gitlab.rtems.org/rtems/pkg/rtems-lwip/-/merge_requests/37#note_149379

 > +#define MEM_SIZE (64 * 1024)
 > +#define PBUF_POOL_SIZE 16
 > +
 > +/* LwIP context and resource adjustments */
 > +#define LWIP_NETIF_LINK_CALLBACK 1
 > +#define MEMP_NUM_NETCONN 32
 > +#define MEMP_NUM_TCP_PCB_LISTEN 16
 > +
 > +#define LWIP_DEBUG 0
 > +#define IP_DEBUG LWIP_DBG_OFF
 > +#define ETHARP_DEBUG LWIP_DBG_OFF
 > +#define ICMP_DEBUG LWIP_DBG_OFF
 > +#define UDP_DEBUG LWIP_DBG_OFF
 > +#define TCP_DEBUG LWIP_DBG_OFF
 > +
 > +#define LWIP_ICMP 1

Most of those settings were indeed user tunables and have been removed. However, `MEM_SIZE` and `PBUF_POOL_SIZE` turned out to be hardware requirements: the `lwipopts.h` defaults of `PBUF_POOL_SIZE=512` and `MEM_SIZE=2MB` cause an \~850 KB BSS section which overflows the STM32H7's 512 KB AXI SRAM at link time. These values are constrained by the hardware, not by developer preference.

-- 
View it on GitLab: https://gitlab.rtems.org/rtems/pkg/rtems-lwip/-/merge_requests/37#note_149379
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