rb_tree: restore binary compat w/ 13

A change to RB_COLOR_INSERT, when merged into stable/13, broke binary
compatibility. For 13, call the new function RB_DO_COLOR_INSERT, and
restore the old function with the original name and parameters. Define
RB_COLOR_INSERT in tree.h, and remove changes to the linux rbtree
header.

Another change altered the order of pointers in the RB_ENTRY struct.
For 13, restore the original order.

Reported by: manu
Reviewed by: hselasky
Tested by: manu
Differential Revision: https://reviews.freebsd.org/D37716