regen_makefile.sh: set executable name explicitly

Set the executable name in each regen_makefile.sh explicitly with -e,
instead of having it set indirectly from the first .ttcn file. Make it
consistent by placing the name on top of each of these files.

Fix for warning:
ttcn3_makefilegen: warning: File `BSC_Tests.ttcn' was given more than once for the Makefile.

Related: OS#5252
Change-Id: I5ed03f8f3ed905483620dc7bae33b617bbb8507f
diff --git a/bsc-nat/regen_makefile.sh b/bsc-nat/regen_makefile.sh
index 33b557c..470d109 100755
--- a/bsc-nat/regen_makefile.sh
+++ b/bsc-nat/regen_makefile.sh
@@ -1,6 +1,6 @@
 #!/bin/sh
 
-MAIN=BSCNAT_Tests.ttcn
+NAME=BSCNAT_Tests
 
 FILES="
 	*.c
@@ -29,4 +29,4 @@
 	-DUSE_MTP3_DISTRIBUTOR
 "
 
-../regen-makefile.sh $MAIN $FILES
+../regen-makefile.sh -e $NAME $FILES