Fix generation with chip_with_lwip=false (#5206)
Fix generation with chip_with_lwip=false (#5206)

This fixes the following error if LwIP is removed from the build:

  ERROR at //src/lwip/BUILD.gn:23:1: Assertion failed.
  assert(chip_with_lwip)
  ^-----
  See //BUILD.gn:73:7: which caused the file to be included.
	"${chip_root}/src/lwip:all",
	^--------------------------

The problem is just that we're not checking chip_with_lwip at the top
level.
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