fix gen_links.sh: don't include source dir as link target

First of all, use one common place to define the gen_links() macro, in
gen_links.sh.inc.

In this new file, add a 'shift' to exclude the $DIR arg from also appearing in
$FILES.

This prevents the following wrong symlinks in the source dirs:

  M3UA_CNL113537/src/src
  MTP3asp_CNL113337/src/src
  SCCP_CNL113341/src/src

Change-Id: Ia8493e77df1ba8723f2c5d2a49816247b0fb55f7
diff --git a/selftest/gen_links.sh b/selftest/gen_links.sh
index b0b2688..542e3c2 100755
--- a/selftest/gen_links.sh
+++ b/selftest/gen_links.sh
@@ -2,14 +2,7 @@
 
 BASEDIR=../deps
 
-gen_links() {
-	DIR=$1
-	FILES=$*
-	for f in $FILES; do
-		echo "Linking $f"
-		ln -sf $DIR/$f $f
-	done
-}
+. ../gen_links.sh.inc
 
 #DIR=$BASEDIR/titan.TestPorts.UNIX_DOMAIN_SOCKETasp/src
 #FILES="UD_PT.cc  UD_PT.hh  UD_PortType.ttcn  UD_Types.ttcn"