mainline kernel and preferred kernel

[farinet at arcor.de]

Since i found somewhere - to resolve my a2dp problem - the suggestion to
try with the 3.15 mainline kernel, i installed this. The kernel works
fine so far, but that specific problem, for me at least, isn't solved by
it. Now, in the grub menu, the mainline kernel is the topmost (i do not
like to remove it, since together with the 3.13 kernel it's the only one
i have and i prefer to have at least 2, to have an alternative in case
of problems) but i would like to start by default in the default kernel.

How is this done (by modifying grub, i presume??), if it can be done?