hcxdumptool: pass TARGET_LDFLAGS and restore -std=gnu99

Command-line CFLAGS overrides upstream's CFLAGS += -std=gnu99.
Pass TARGET_LDFLAGS for OpenWrt PIE/RELRO, and keep -lpcap which that
override would otherwise drop.

Signed-off-by: Atanas Vladimirov <vladimirov.atanas@gmail.com>

net/hcxdumptool/Makefile

@@ -41,7 +41,8 @@ endef
 define Build/Compile
 	$(MAKE) -C $(PKG_BUILD_DIR)/ \
 		$(TARGET_CONFIGURE_OPTS) \
-		CFLAGS="$(TARGET_CFLAGS)" \
+		CFLAGS="$(TARGET_CFLAGS) -std=gnu99" \
+		LDFLAGS="$(TARGET_LDFLAGS) -lpcap" \
 		hcxdumptool
 endef