alpha: Don't export SOCK_NONBLOCK to user space.

commit a2fa3ccd7b43665fe14cb562761a6c3d26a1d13f upstream.

Currently we export SOCK_NONBLOCK to user space but that conflicts with
the definition from glibc leading to compilation errors in user programs
(e.g.  see Debian bug #658460).

The generic socket.h restricts the definition of SOCK_NONBLOCK to the
kernel, as does the MIPS specific socket.h, so let's do the same on
Alpha.

Signed-off-by: Michael Cree <mcree@orcon.net.nz>
Acked-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>