[LWIP] CubeMX Issues

[Rado1]

HI,

Had to make some config changes, but CubeMX will not allow.

 CubeMx 6.17 and LWIP 2.2.1:

1. MEM ALIGNMENT - only 2 or 4 (need 32 for STM32H7)

2. PBUF_POOL_SIZE - can't be set to 0. 

3.  file: cc.h - overriden by CubeMx generation code. 

per lwip repo isntructions:

* To relocate a pool, declare it as extern in cc.h. Example for GCC: 
* extern u8_t \_\_attribute\_\_((section(".onchip_mem"))) memp_memory_my_private_pool_base[];