Hello Sushain,
Is it really required to declare the pools in lwipopts.h? memp_std.h contains pools used by lwIP itself. Private pools are only useful in your own sources, which can include a different header (so no need to declare them in lwipopts.h).
Check the HTTP server (src/apps/httpd/httpd.c) for an example of "private" memory pools declaration and usage. To declare/use your own pool, you just need to include memp.h