Enable Checkstyle for "repo upload" for more projects.

This CL enables Checkstyle for the following directories:
- wifi/

Bug: 28291425
Test: Compilation
Change-Id: Iefdabcc3c5867f392c0bf9925d10ddeb3b334c9f
diff --git a/PREUPLOAD.cfg b/PREUPLOAD.cfg
index 1f8ab21..c74516d 100644
--- a/PREUPLOAD.cfg
+++ b/PREUPLOAD.cfg
@@ -8,6 +8,7 @@
                       services/print/
                       services/usb/
                       telephony/
+                      wifi/
 
 api_lint_hook = ${REPO_ROOT}/frameworks/base/tools/apilint/apilint_sha.sh ${PREUPLOAD_COMMIT}