And additional to the solution given you above, when you have such questions, you could try to find out if YaST can help you. In the above case YaST > System > Bootloader would bring you to a window with all your GRUB entries. Selecting one for changing wil present the entry to you in a nice split up manner where the parameters are in the last line. You will now understand that adding there and confirming your changes will do the trick also.
Not a bad idea to spend some leftover time is to go through YaST’s possibilities. Do not change things, but get an idea about the possibilities.