Fix strdup-related memory leak in nr-softmodem

* strdup is returning a malloced string which needs to be freed after use

> Direct leak of 90 byte(s) in 1 object(s) allocated from:
	> 0 0x7ffff745b9a7 in __interceptor_strdup ../../../../src/libsanitizer/asan/asan_interceptors.cpp:454
	> 1 0x5555591598a3 in main /executables/nr-softmodem.c:667
	> 2 0x7ffff5e29d8f in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58

executables/nr-softmodem.c

@@ -664,7 +664,8 @@ int main( int argc, char **argv ) {
 #define PACKAGE_VERSION "UNKNOWN-EXPERIMENTAL"
 #endif
   // strdup to put the sring in the core file for post mortem identification
-  LOG_I(HW, "Version: %s\n", strdup(PACKAGE_VERSION));
+  char *pckg = strdup(PACKAGE_VERSION);
+  LOG_I(HW, "Version: %s\n", pckg);
 
   // don't create if node doesn't connect to RRC/S1/GTP
   const ngran_node_t node_type = get_node_type();
@@ -819,6 +820,7 @@ int main( int argc, char **argv ) {
       RC.ru[ru_id]->ifdevice.trx_end_func(&RC.ru[ru_id]->ifdevice);
   }
 
+  free(pckg);
   logClean();
   printf("Bye.\n");
   return 0;