Add conditional compilation about IPv6 sources and headers, change code style

correct netconn API usage

fix:comment spelling mistake

[net] Add lwIP head porting to fetch lwIP new feature, for example IPv4/v6 dual stack.

tools/keil: preserve the order of CPPPATH

The order of CPPPATH is important: some project would use the order of
CPPPATH to override the default configuration headers. This commit also
refine the this piece of code in a more Pythonic way.

[finsh] fixed finsh issue.

relation=>relocation

kernel: mempool: fix race condition in rt_mp_alloc

When thread wake up from waiting for memory, there is a chance that
there is no memory available in high pressure. So use a loop to check
again. Otherwise, there will be a NULL reference.

Ls1b

[BSP]BM9BF618S:fix timer initialization issue.