Fix memory leak in nr-uesoftmodem

* strdup is returning a malloced string that needs to 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 0x555556c7b341 in main /executables/nr-uesoftmodem.c:461
    >2 0x7ffff5e29d8f in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58

executables/nr-uesoftmodem.c

@@ -458,7 +458,8 @@ 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);
 
   PHY_vars_UE_g = malloc(sizeof(*PHY_vars_UE_g) * NB_UE_INST);
   for (int inst = 0; inst < NB_UE_INST; inst++) {
@@ -593,6 +594,7 @@ int main(int argc, char **argv)
     }
   }
 
+  free(pckg);
   return 0;
 }