dnsdist: add missing build dep on protoc

The build needs protoc, otherwise it fails.

checking if we need to link in protobuf... yes
checking for PROTOBUF... yes
checking for protoc... no
configure: error: Protobuf requested but the protobuf compiler was not found

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>

net/dnsdist/Makefile

@@ -15,6 +15,8 @@ PKG_CPE_ID:=cpe:/a:powerdns:dnsdist
 
 PKG_INSTALL:=1
 
+PKG_BUILD_DEPENDS:=protobuf/host
+
 PKG_CONFIG_DEPENDS:= \
   CONFIG_DNSDIST_GNUTLS \
   CONFIG_DNSDIST_OPENSSL