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/sip/regen_makefile.sh b/sip/regen_makefile.sh
index caf657c..c7a645d 100755
--- a/sip/regen_makefile.sh
+++ b/sip/regen_makefile.sh
@@ -1,5 +1,7 @@
 #!/bin/sh
 
+NAME=SIP_Tests
+
 FILES="
 	*.c
 	*.ttcn
@@ -24,4 +26,4 @@
 	-DRAN_EMULATION_CTRL
 "
 
-../regen-makefile.sh SIP_Tests.ttcn $FILES
+../regen-makefile.sh -e $NAME $FILES