[lwip] Fix build with ccache

When building with ccache  and -Werror option imposed by fuchsia BUILD.gn
results in error due to -Wparentheses-equality and  -Wpointer-bool-conversion
caused by the way ccache treats macro expansions.
Any future warning causing build to fail could be easily added.

Change-Id: Ib051a4627bf913fe61db63839e5d7e7076863053
1 file changed