Fix a missing unlock operation in interrupt handler.
Fix a missing unlock operation in interrupt handler.

PR:		kern/99205
Submitted by:	Alexey Illarionov <littlesavage AT rambler DOT ru>
MFC after:	1 week

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase