build:kernel: use variable to store version

This way, next time we want to update the kernel we have just to change
the version without touching too much the code

Signed-off-by: Federico Vaga <federico.vaga@cern.ch>

build/scripts/wrs_build_kernel

 #!/bin/bash
 
+KERVER=2.6.39
+
 # check variables, like all scripts herein do
 WRS_SCRIPT_NAME=$(basename $0)
 if [ -z "$WRS_BASE_DIR" ]; then
@@ -11,8 +13,8 @@ fi
 wrs_check_vars WRS_OUTPUT_DIR WRS_DOWNLOAD_DIR CROSS_COMPILE
 
 wrs_echo "--- Linux kernel for switch"
-tarname="linux-2.6.39.tar.bz2"
-patchdir="${WRS_BASE_DIR}/../patches/kernel/v2.6.39"
+tarname="linux-${KERVER}.tar.bz2"
+patchdir="${WRS_BASE_DIR}/../patches/kernel/v${KERVER}"
 wrs_download $tarname
 
 mkdir -p $WRS_OUTPUT_DIR/build || wrs_die "mkdir build"
@@ -20,7 +22,7 @@ mkdir -p $WRS_OUTPUT_DIR/images || wrs_die "mkdir images"
 
 # go to the build dir and compile it, using our configuration
 cd $WRS_OUTPUT_DIR/build
-dirname="linux-2.6.39"
+dirname="linux-${KERVER}"
 rm -rf $dirname
 tar xjf ${WRS_DOWNLOAD_DIR}/$tarname || wrs_die "untar $tarname"
 
@@ -48,7 +50,7 @@ make oldconfig  || wrs_die "kernel config"
 
 make $WRS_MAKE_J zImage modules  || wrs_die "kernel compilation"
 
-mkdir -p $WRS_OUTPUT_DIR/images/lib/modules/2.6.39/kernel
+mkdir -p $WRS_OUTPUT_DIR/images/lib/modules/$KERVER/kernel
 
-cp $(find . -name '*.ko') $WRS_OUTPUT_DIR/images/lib/modules/2.6.39/kernel
+cp $(find . -name '*.ko') $WRS_OUTPUT_DIR/images/lib/modules/$KERVER/kernel
 cp arch/$ARCH/boot/zImage $WRS_OUTPUT_DIR/images