Add exported includes to libwpa_client

This is the first step to removing LOCAL_COPY_HEADERS in this module,
and is sufficient to replace the use in frameworks/opt/net/wifi. Once
all the other users as satisfied, the LOCAL_COPY_HEADERS will be
removed.

Test: lunch aosp_angler-eng; m -j native
Change-Id: Iab5736cfdb4652933d44b66acf247f5e57b6e344
3 files changed