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/build_oai

@@ -448,6 +448,11 @@ function main() {
         flash_firmware_bladerf
       fi
     fi
+    if [ "$FLEXRAN_AGENT" == "1" ] ; then
+      echo_info "installing protobuf/protobuf-c for flexran agent support"
+      install_protobuf_from_source
+      install_protobuf_c_from_source
+    fi
   fi
 
   if [ "$INSTALL_OPTIONAL" = "1" ] ; then

cmake_targets/tools/build_helper

@@ -184,10 +184,14 @@ 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`
@@ -410,8 +414,6 @@ 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

openair2/ENB_APP/MESSAGES/V2/config_common.proto

-//'syntax = "proto2";'
+syntax = "proto2";
 package protocol;
 
 //

openair2/ENB_APP/MESSAGES/V2/config_messages.proto

-//'syntax = "proto2";'
+syntax = "proto2";
 package protocol;
 
 import "config_common.proto";

openair2/ENB_APP/MESSAGES/V2/control_delegation.proto

-//'syntax = "proto2";'
+syntax = "proto2";
 package protocol;
 
 enum flex_control_delegation_type {

openair2/ENB_APP/MESSAGES/V2/controller_commands.proto

+syntax = "proto2";
 package protocol;
 
 import "mac_primitives.proto";

openair2/ENB_APP/MESSAGES/V2/flexran.proto

-//'syntax = "proto2";' 
+syntax = "proto2";
 package protocol;
 
 import "stats_messages.proto";
@@ -40,7 +40,7 @@ enum flexran_direction {
 }
 	
 enum flexran_err {
-        option allow_alias = true;
+        //option allow_alias = true;
 	// message errors
 	NO_ERR = 0;	
 	MSG_DEQUEUING = -1;

openair2/ENB_APP/MESSAGES/V2/header.proto

+syntax = "proto2";
 package protocol;
 
 message flex_header {

openair2/ENB_APP/MESSAGES/V2/mac_primitives.proto

+syntax = "proto2";
 package protocol;
 
 //

openair2/ENB_APP/MESSAGES/V2/stats_common.proto

+syntax = "proto2";
 package protocol;
 
 //

openair2/ENB_APP/MESSAGES/V2/stats_messages.proto

+syntax = "proto2";
 package protocol;
 
 //import "header.proto";

openair2/ENB_APP/MESSAGES/V2/time_common.proto

+syntax = "proto2";
 package protocol;
 
 enum flex_harq_status {