wallet: warn if lockable memory limit is too low

src/common/util.cpp

@@ -728,6 +728,21 @@ std::string get_nix_version_display_string()
     return true;
   }
 
+  ssize_t get_lockable_memory()
+  {
+#ifdef __GLIBC__
+    struct rlimit rlim;
+    if (getrlimit(RLIMIT_MEMLOCK, &rlim) < 0)
+    {
+      MERROR("Failed to determine the lockable memory limit");
+      return -1;
+    }
+    return rlim.rlim_cur;
+#else
+    return -1;
+#endif
+  }
+
   bool on_startup()
   {
     mlog_configure("", true);