wifi: Add utility for struct conversions

Add a new utility file (hidl_struct_util) which would contain helper
functions to convert legacy HAL structures to HIDL structures and vice
versa.
Added utility functions to convert:
1. Background scan params from HIDL to legacy.
2. Scan Result from legacy to HIDL.
3. Cached Scan results from legacy to HIDL.
4. Link layer stats from legacy to HIDL.

Bug: 31991459
Test: Compiles
Change-Id: I48a49b43d425f8cc3059241c4bd652b2346f2381
diff --git a/wifi/1.0/default/Android.mk b/wifi/1.0/default/Android.mk
index 62d2e0b..931a314 100644
--- a/wifi/1.0/default/Android.mk
+++ b/wifi/1.0/default/Android.mk
@@ -18,6 +18,7 @@
 LOCAL_MODULE_RELATIVE_PATH := hw
 LOCAL_CPPFLAGS := -Wall -Wno-unused-parameter -Werror -Wextra
 LOCAL_SRC_FILES := \
+    hidl_struct_util.cpp \
     service.cpp \
     wifi.cpp \
     wifi_ap_iface.cpp \