recv.2, cmsg.3, unix.7: global fix: s/UNIX socket/UNIX doamin socket/

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/recv.2

@@ -356,7 +356,7 @@ Ancillary data should only be accessed by the macros defined in
 .BR cmsg (3).
 .PP
 As an example, Linux uses this ancillary data mechanism to pass extended
-errors, IP options, or file descriptors over UNIX sockets.
+errors, IP options, or file descriptors over UNIX domain sockets.
 .PP
 The
 .I msg_flags

man3/cmsg.3

@@ -185,7 +185,8 @@ if (cmsg == NULL) {
 .fi
 .in
 .PP
-The code below passes an array of file descriptors over a UNIX socket using
+The code below passes an array of file descriptors over a
+UNIX domain socket using
 .BR SCM_RIGHTS :
 .PP
 .in +4n

man7/unix.7

@@ -31,7 +31,7 @@ The
 .BR AF_LOCAL )
 socket family is used to communicate between processes on the same machine
 efficiently.
-Traditionally, UNIX sockets can be either unnamed,
+Traditionally, UNIX domain sockets can be either unnamed,
 or bound to a file system pathname (marked as being of type socket).
 Linux also supports an abstract namespace which is independent of the
 file system.
@@ -48,7 +48,7 @@ and (since Linux 2.6.4)
 for a connection-oriented socket that preserves message boundaries
 and delivers messages in the order that they were sent.
 
-UNIX sockets support passing file descriptors or process credentials
+UNIX domain sockets support passing file descriptors or process credentials
 to other processes using ancillary data.
 .SS Address Format
 A UNIX domain socket address is represented in the following structure:
@@ -398,7 +398,7 @@ Creation of a new socket will fail if the process does not have write and
 search (execute) permission on the directory the socket is created in.
 Connecting to the socket object requires read/write permission.
 This behavior differs from many BSD-derived systems which
-ignore permissions for UNIX sockets.
+ignore permissions for UNIX domain sockets.
 Portable programs should not rely on
 this feature for security.