r347197 contained an MFC for r332389, adding the STATE_LOCK to the iflib
core driver. Unfortunately, the commit accidentally missed adding the
Without this, if you build a STABLE-11 kernel with INVARIANTS enabled,
any mtx_lock of the state lock will result in a panic:
panic: mtx_lock() of spin mutex (null) @ /usr/src/sys/net/iflib.c:5522
It actually ends up looking like a panic due to taking a spin mutex when
we could be interrupted. However, the real cause is because the lock
class was never initialized.
Initialize the STATE_LOCK properly during iflib_register to fix this.