Define enum for so_qstate outside of struct.

LLVM-9.0 clang++ throws an error for enum defined within
an anonymous struct.

Reviewed by:	jtl, rpokala
MFC after:	1 week
Differential Revision: https://reviews.freebsd.org//D24477

sys/sys/socketvar.h

@@ -67,6 +67,12 @@ typedef	void so_dtor_t(struct socket *);
 
 struct socket;
 
+enum socket_qstate {
+	SQ_NONE = 0,
+	SQ_INCOMP = 0x0800,	/* on sol_incomp */
+	SQ_COMP = 0x1000,	/* on sol_comp */
+};
+
 /*-
  * Locking key to struct socket:
  * (a) constant after allocation, no locking required.
@@ -122,12 +128,7 @@ struct socket {
 			/* (e) Our place on accept queue. */
 			TAILQ_ENTRY(socket)	so_list;
 			struct socket		*so_listen;	/* (b) */
-			enum {
-				SQ_NONE = 0,
-				SQ_INCOMP = 0x0800,	/* on sol_incomp */
-				SQ_COMP = 0x1000,	/* on sol_comp */
-			}			so_qstate;	/* (b) */
-
+			enum socket_qstate so_qstate;		/* (b) */
 			/* (b) cached MAC label for peer */
 			struct	label		*so_peerlabel;
 			u_long	so_oobmark;	/* chars to oob mark */