[RESTRICT AUTOMERGE] Undefine NAN before defining it again

After upgrading libc++, math.h happens to be included at the point
where this file tries to define NAN. Redefining a macro to a different
value is an error, but #undef'ing a macro is OK even if the macro isn't
actually defined.

Bug: b/175635923
Test: treehugger
Change-Id: Ie8e3e87189bcd7ed8fccccfc0a79e04a5bfda16b
Merged-In: Ie8e3e87189bcd7ed8fccccfc0a79e04a5bfda16b
diff --git a/wifi/1.6/default/wifi_feature_flags.cpp b/wifi/1.6/default/wifi_feature_flags.cpp
index e80a3cd..ff23e7c 100644
--- a/wifi/1.6/default/wifi_feature_flags.cpp
+++ b/wifi/1.6/default/wifi_feature_flags.cpp
@@ -136,6 +136,7 @@
 #define AP IfaceConcurrencyType::AP
 #define AP_BRIDGED IfaceConcurrencyType::AP_BRIDGED
 #define P2P IfaceConcurrencyType::P2P
+#undef NAN  // undefine NAN from math.h
 #define NAN IfaceConcurrencyType::NAN
 static const std::vector<V1_6::IWifiChip::ChipMode> kChipModesPrimary{
         {kMainModeId, ChipConcurrencyCombination::make_vec({WIFI_HAL_INTERFACE_COMBINATIONS})},