Regression in 32-bit-compat TIOCGPTPEER ioctl due to 311fc65c9fb9c966bca8e6f3ff8132ce57344ab9

[Robert O'Callahan]

This commit refactored the implementation of TIOCGPTPEER, moving "case
TIOCGPTPEER" from pty_unix98_ioctl() to tty_ioctl().
pty_unix98_ioctl() is called by pty_unix98_compat_ioctl(), so before
the commit, TIOCGPTPEER worked for 32-bit userspace. Unfortunately
tty_compat_ioctl() does not call tty_ioctl() so after the commit,
TIOCGPTPEER from 32-bit userspace fails with ENOTTY.

Testcase in https://bugzilla.kernel.org/show_bug.cgi?id=202271.

I found this bug running the rr test suite.

Rob
-- 
Su ot deraeppa sah dna Rehtaf eht htiw saw hcihw, efil lanrete eht uoy
ot mialcorp ew dna, ti ot yfitset dna ti nees evah ew; deraeppa efil
eht. Efil fo Drow eht gninrecnoc mialcorp ew siht - dehcuot evah sdnah
ruo dna ta dekool evah ew hcihw, seye ruo htiw nees evah ew hcihw,
draeh evah ew hcihw, gninnigeb eht morf saw hcihw taht.