Enable Checkstyle for "repo upload" for more projects.

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

Bug: 28291425
Test: Compilation
Change-Id: Iefdabcc3c5867f392c0bf9925d10ddeb3b334c9f

PREUPLOAD.cfg

@@ -8,6 +8,7 @@ checkstyle_hook = ${REPO_ROOT}/prebuilts/checkstyle/checkstyle.py --sha ${PREUPL
                       services/print/
                       services/usb/
                       telephony/
+                      wifi/
 
 api_lint_hook = ${REPO_ROOT}/frameworks/base/tools/apilint/apilint_sha.sh ${PREUPLOAD_COMMIT}