Revert lock changes inside ifioctl_get()

Revert lock changes inside ifioctl_get()

WITNESS isn't happy with r1.667 "Push kernel lock into ifioctl_get()", so
revert it (including r1.668 and r1.669 depending on it):

	witness: userret: returning with the following locks held:
	exclusive kernel_lock &kernel_lock r = 0 (0xffffffff82455f58)
	#0  witness_lock+0x311
	#1  ifioctl_get+0x2e
	#2  sys_ioctl+0x2c4
	#3  syscall+0x384
	#4  Xsyscall+0x128
	panic: witness_warn
	Stopped at      db_enter+0x10:  popq    %rbp
	    TID    PID    UID     PRFLAGS     PFLAGS  CPU  COMMAND
	* 70588  52613      0         0x3          0    4K pfctl

So back to the drawing board while leaving documentation bits (r1.670).
Thanks Hrvoje.