hotfix: protobuf-c compilation failure

protobuf-c does not compile anymore.

Let's handle this a bit better.

We now install protobuf and protobuf-c only for the
flexran agent. That is, if you want to use the flexran
agent, you need to install protobuf/protobuf-c and
you do it this way:

  ./build_oai -I -a

(you add -a)

Other targets don't need protobuf nor protobuf-c, so
it's not installed by the -I command of build_oai,
unless you pass -a with -I.

Also, we now use protobuf 3.3.0, not 2.6.1. The code
has been adapted, a quick test seems to indicate that
the system works, but it has not been intensively tested.

cmake_targets/tools/build_helper

@@ -202,10 +202,14 @@ install_protobuf_from_source(){
     (
     cd /tmp
     echo "Downloading protobuf"
-    rm -rf /tmp/protobuf-2.6.1.tar.gz* /tmp/protobuf-2.6.1
-    wget https://github.com/google/protobuf/releases/download/v2.6.1/protobuf-2.6.1.tar.gz
-    tar -xzvf protobuf-2.6.1.tar.gz --owner $USER --group $USER --no-same-owner 
-    cd protobuf-2.6.1/
+    #rm -rf /tmp/protobuf-2.6.1.tar.gz* /tmp/protobuf-2.6.1
+    #wget https://github.com/google/protobuf/releases/download/v2.6.1/protobuf-2.6.1.tar.gz
+    #tar -xzvf protobuf-2.6.1.tar.gz --owner $USER --group $USER --no-same-owner
+    #cd protobuf-2.6.1/
+    rm -rf /tmp/protobuf-cpp-3.3.0.tar.gz* /tmp/protobuf-3.3.0
+    wget https://github.com/google/protobuf/releases/download/v3.3.0/protobuf-cpp-3.3.0.tar.gz
+    tar -xzvf protobuf-cpp-3.3.0.tar.gz --owner $USER --group $USER --no-same-owner
+    cd protobuf-3.3.0/
     ./configure
     echo "Compiling protobuf"
     make -j`nproc`
@@ -641,8 +645,6 @@ check_install_oai_software() {
     install_asn1c_from_source
     $SUDO rm -fr /opt/ssh
     $SUDO git clone https://gist.github.com/2190472.git /opt/ssh
-    install_protobuf_from_source
-    install_protobuf_c_from_source
 }
 
 ### Remove Nettle installation which was done from sources (only done for Ubuntu Distro)