mq_open.3: Rework details in Eugene Syromyatnikov's patch

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

man3/mq_open.3

@@ -119,18 +119,25 @@ as for
 The permissions settings are masked against the process umask.
 
 The
+.I mq_maxmsg
+and
+.I mq_msgsize
+fields of the
+.IR "struct mq_attr"
+pointed to by the
 .I attr
-argument specifies attributes for the queue.
+argument specify attributes for the queue.
 See
 .BR mq_getattr (3)
-for details (except for
+for details.
+(Note that the
 .I mq_flags
-field which is currently ignored by
-.BR mq_open() ;
+field in that structure is ignored by
+.BR mq_open ();
+the
 .B O_NONBLOCK
-flag should be set in
-.I oflag
-parameter instead).
+flag is instead set via
+.IR oflag .)
 If
 .I attr
 is NULL, then the queue is created with implementation-defined