af_unix: Kconfig: make CONFIG_UNIX bool

Let's make CONFIG_UNIX a bool instead of a tristate.
We've decided to do that during discussion about SCM_PIDFD patchset [1].

[1] https://lore.kernel.org/lkml/[email protected]/

Cc: "David S. Miller" <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Cc: Paolo Abeni <[email protected]>
Cc: Leon Romanovsky <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Kuniyuki Iwashima <[email protected]>
Cc: Lennart Poettering <[email protected]>
Cc: Luca Boccassi <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Suggested-by: Jakub Kicinski <[email protected]>
Signed-off-by: Alexander Mikhalitsyn <[email protected]>
Acked-by: Christian Brauner <[email protected]>
Reviewed-by: Eric Dumazet <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

net/unix/Kconfig

@@ -4,7 +4,7 @@
 #
 
 config UNIX
-	tristate "Unix domain sockets"
+	bool "Unix domain sockets"
 	help
 	  If you say Y here, you will include support for Unix domain sockets;
 	  sockets are the standard Unix mechanism for establishing and
@@ -14,10 +14,6 @@ config UNIX
 	  an embedded system or something similar, you therefore definitely
 	  want to say Y here.
 
-	  To compile this driver as a module, choose M here: the module will be
-	  called unix.  Note that several important services won't work
-	  correctly if you say M here and then neglect to load the module.
-
 	  Say Y unless you know what you are doing.
 
 config UNIX_SCM