Correct LWIP_DEBUG definition
Correct LWIP_DEBUG definition

Commit f602c936 incorrectly started defining LWIP_DEBUG as either 0 or
1.

lwipopts.h locally was changed to use #if, but all existing users
continued to use #ifdef. Therefore defining it to 0 was accidentally
enabling it for quite a few users.

This would have pulled in some unwanted lwIP code, and affected some
drivers, eg k64f_emac.c allocating an extra 2K of stack.

Correct lwipopts.h to either define it as 1 or leave it undefined, and
change the #if tests back to #ifdef, so all are consistent.

HeadsUpDisplayInc/mbed,nRFMesh/mbed-os,ryankurte/mbed-os,kjbracey-arm/mbed,karsev/mbed-os,Archcady/mbed-os,mbedmicro/mbed,HeadsUpDisplayInc/mbed,mazimkhan/mbed-os,infinnovation/mbed-os,kjbracey-arm/mbed,HeadsUpDisplayInc/mbed,catiedev/mbed-os,c1728p9/mbed-os,mazimkhan/mbed-os,ryankurte/mbed-os,ryankurte/mbed-os,andcor02/mbed-os,YarivCol/mbed-os,catiedev/mbed-os,catiedev/mbed-os,andcor02/mbed-os,ryankurte/mbed-os,nRFMesh/mbed-os,svogl/mbed-os,mazimkhan/mbed-os,kjbracey-arm/mbed,YarivCol/mbed-os,CalSol/mbed,CalSol/mbed,infinnovation/mbed-os,Archcady/mbed-os,svogl/mbed-os,ryankurte/mbed-os,mazimkhan/mbed-os,YarivCol/mbed-os,karsev/mbed-os,mazimkhan/mbed-os,nRFMesh/mbed-os,nRFMesh/mbed-os,andcor02/mbed-os,svogl/mbed-os,YarivCol/mbed-os,svogl/mbed-os,Archcady/mbed-os,YarivCol/mbed-os,betzw/mbed-os,betzw/mbed-os,Archcady/mbed-os,betzw/mbed-os,nRFMesh/mbed-os,betzw/mbed-os,infinnovation/mbed-os,CalSol/mbed,andcor02/mbed-os,CalSol/mbed,catiedev/mbed-os,nRFMesh/mbed-os,betzw/mbed-os,c1728p9/mbed-os,karsev/mbed-os,andcor02/mbed-os,mbedmicro/mbed,infinnovation/mbed-os,karsev/mbed-os,CalSol/mbed,ryankurte/mbed-os,YarivCol/mbed-os,HeadsUpDisplayInc/mbed,catiedev/mbed-os,c1728p9/mbed-os,CalSol/mbed,andcor02/mbed-os,mbedmicro/mbed,infinnovation/mbed-os,mazimkhan/mbed-os,svogl/mbed-os,c1728p9/mbed-os,karsev/mbed-os,mbedmicro/mbed,mbedmicro/mbed,karsev/mbed-os,c1728p9/mbed-os,Archcady/mbed-os,svogl/mbed-os,c1728p9/mbed-os,HeadsUpDisplayInc/mbed,Archcady/mbed-os,kjbracey-arm/mbed,HeadsUpDisplayInc/mbed,catiedev/mbed-os,infinnovation/mbed-os,betzw/mbed-os