Don't map LINUX_POSIX_VDISABLE to _POSIX_VDISABLE and vice versa for
the VMIN and VTIME members of the c_cc array. These members are not
special control characters. By not excluding these members we
changed the noncanonical mode input processing when both members
were 0 on entry (=LINUX_POSIX_VDISABLE) as we would remap them to 255
(=_POSIX_VDISABLE). See termios(4) case A for how that screws up
your terminal I/O.

PR: 23173
Originator: Bjarne Blichfeldt <bbl@dk.damgaard.com>
Patch by: Boris Nikolaus <bn@dali.tellique.de> (original submission)

	  Philipp Mergenthaler <philipp.mergenthaler@stud.uni-karlsruhe.de>

Reminders by: Joseph Holland King <gte743n@cad.gatech.edu>
MFC after: 5 days