Fix an assertion when if_down()ing a ALTQ managed interface. The lock should have been in place all the time the mtx_assert in the ALTQ code just discovered the shortcoming.
Fix an assertion when if_down()ing a ALTQ managed interface. The lock should
have been in place all the time the mtx_assert in the ALTQ code just
discovered the shortcoming.

PR:		i386/71195
Tested by:	Bettan (PR originator), myself
MFC after:	5 days

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