stubby: explicitly disable static linking

Although undocumented, there's a way to explicitly disable static linking in
Stubby, setting the CMake build option ENABLE_GETDNS_STATIC_LINK to OFF (ON by
default). Make it so.

Signed-off-by: Rui Salvaterra <rsalvaterra@gmail.com>

net/stubby/Makefile

@@ -6,7 +6,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=stubby
 PKG_VERSION:=0.4.0
-PKG_RELEASE:=5
+PKG_RELEASE:=6
 
 PKG_SOURCE_PROTO:=git
 PKG_SOURCE_URL:=https://github.com/getdnsapi/$(PKG_NAME)
@@ -45,6 +45,9 @@ define Package/stubby/conffiles
 /etc/config/stubby
 endef
 
+# Disable static linking
+CMAKE_OPTIONS += -DENABLE_GETDNS_STATIC_LINK=OFF
+
 define Package/stubby/install
 	$(INSTALL_DIR) $(1)/usr/sbin
 	$(INSTALL_BIN) $(PKG_INSTALL_DIR)/usr/bin/stubby $(1)/usr/sbin/stubby