kamcmd: Makefile - use CUSTOM_NAME for specifying custom binary name

- previous use of NAME can clash with environment variable NAME that
  could be set by OS or by Kamailio modules installation
- GH #3628

utils/kamcmd/Makefile

@@ -8,10 +8,15 @@ include $(COREPATH)/Makefile.targets
 auto_gen=
 RELEASE=1.5
 UTIL_SRC_NAME=kamcmd
+# Pass CUSTOM_NAME to overwrite the kamcmd/sercmd bin name
+ifeq ($(CUSTOM_NAME),)
 ifeq ($(FLAVOUR),ser)
-	NAME?=sercmd
+	NAME=sercmd
 else
-	NAME?=kamcmd
+	NAME=kamcmd
+endif
+else
+	NAME=$(CUSTOM_NAME)
 endif
 
 readline_localpath=$(LOCALBASE)/include/readline/readline.h