utils/sercmd: set SRNAME at compile time

- it is set to sip server name (e.g., ser, kamailio)
- it is used to build the default path to ctl file used to communicate
  with sip server via ctl module
- reported by Henning Westerholt
(cherry picked from commit 1b58b26b7ccf7b2c01185a22ad076a3655e43664)

utils/sercmd/Makefile

@@ -22,7 +22,7 @@ endif #ifneq (,$(MAKECMDGOALS))
 
 # erase common DEFS (not needed)
 C_DEFS:=
-DEFS:= -DNAME='"$(NAME)"' -DVERSION='"$(RELEASE)"' \
+DEFS:= -DNAME='"$(NAME)"' -DSRNAME='"$(MAIN_NAME)"' -DVERSION='"$(RELEASE)"' \
 		$(filter -D%HAVE -DARCH% -DOS% -D__CPU% -D__OS%, $(DEFS))
 
 # use proper libs (we can't rely on LIBS value since we might be called