[lwip-members] Change wanted in mem.h

[Robert]

I propose that mem.h be recoded as shown below, wrapping the macros in
#ifndef and #endif statements.


#ifndef MEM_ALIGN_SIZE
#define MEM_ALIGN_SIZE(size) (((size) + MEM_ALIGNMENT - 1) & ~(MEM_ALIGNMENT-1))
#endif

#ifndef MEM_ALIGN
#define MEM_ALIGN(addr) ((void *)(((mem_ptr_t)(addr) + MEM_ALIGNMENT - 1) & 
~(mem_ptr_t)(MEM_ALIGNMENT-1)))
#endif


The purpose of this change is to allow someone to define their own macros
for MEM_ALIGN and MEM_ALIGN_SIZE in cc.h if they wish to.  (Actually in my
case, I do need to since my compiler cannot deal with the macros as they
currently exist, hence my modivation for proposing this change.)  Does
anyone have a problem with making this change?

-- 
Best Regards,
Robert