[weave] Enable key export responder support

Bug: 78010
Test: Verified locally that key export request logic is now built.
Change-Id: I468ff686f10844ac07f3bc698ad72c2ab5cb21c0
diff --git a/build/config/fuchsia/WeaveProjectConfig.h b/build/config/fuchsia/WeaveProjectConfig.h
index a951121..4a0c176 100644
--- a/build/config/fuchsia/WeaveProjectConfig.h
+++ b/build/config/fuchsia/WeaveProjectConfig.h
@@ -69,4 +69,7 @@
 
 #define INET_CONFIG_OVERRIDE_SYSTEM_TCP_USER_TIMEOUT 0
 
+// Enable support for handling key export requests.
+#define WEAVE_CONFIG_ENABLE_KEY_EXPORT_RESPONDER 1
+
 #endif /* WEAVEPROJECTCONFIG_H */