Unlock lseek(2).

Unlock lseek(2).

In August 2019 I tried to unlock lseek which failed since the vnode lock
could not be acquired without holding the kernel lock back then.
claudio@ recently made it possible to acquire a vnode lock without
holding the kernel lock. The kernel lock is still required around
VOP_GETATTR() as the underlying file system implementations are not
MP-safe.

ok claudio@