add and use Neighbor::modify_params() convenience function

src/neighbor.cpp

@@ -2356,6 +2356,22 @@ void Neighbor::modify_params(int narg, char **arg)
   }
 }
 
+/* ----------------------------------------------------------------------
+   convenience function to allow modifying parameters from a single string
+------------------------------------------------------------------------- */
+
+void Neighbor::modify_params(const std::string &modcmd)
+{
+  auto args = utils::split_words(modcmd);
+  char **newarg = new char*[args.size()];
+  int i=0;
+  for (const auto &arg : args) {
+    newarg[i++] = (char *)arg.c_str();
+  }
+  modify_params(args.size(),newarg);
+  delete[] newarg;
+}
+
 /* ----------------------------------------------------------------------
    remove the first group-group exclusion matching group1, group2
 ------------------------------------------------------------------------- */