uipc: create dedicated lists for fast and slow timeout callbacks

This avoids having to walk all possible protocols only to check if they
have one (vast majority does not).

Original patch by kevans@.

Reviewed by: kevans
Sponsored by: Rubicon Communications, LLC ("Netgate")

(cherry picked from commit e0a17c3f063fd51430fb2b4f5bc667f79d2967c2)