kernel/isp: Remove two checks which were never true.
Add note about reboot before 'make upgrade' step.

Based on:

http://lists.dragonflybsd.org/pipermail/users/2013-September/090163.html
(cherry picked from commit 43f7fa4fcaec7f2308a0442cf485b180de7b3c1a)
Note on ABI change requiring rebuild of third-party software.

(cherry picked from commit ac04afc3258dcdbfc2072a1df56803905e8bbbad)