Only socantrcvmore() requires socket lock, the rest relies on buffer
locks. Previously, some sockets were designed for socket lock only, so
I intentionally kept it for the entire path to avoid dances around
SB_MTXLOCK. This is not necessary now.

Index: sys/kern/uipc_socket.c
===================================================================
RCS file: /cvs/src/sys/kern/uipc_socket.c,v
retrieving revision 1.364
diff -u -p -r1.364 uipc_socket.c
--- sys/kern/uipc_socket.c	23 Jan 2025 10:44:13 -0000	1.364
+++ sys/kern/uipc_socket.c	26 Jan 2025 10:13:26 -0000
@@ -1278,13 +1278,13 @@ sorflush(struct socket *so)
 
 	solock_shared(so);
 	socantrcvmore(so);
+	sounlock_shared(so);
 	mtx_enter(&sb->sb_mtx);
 	m = sb->sb_mb;
 	memset(&sb->sb_startzero, 0,
 	     (caddr_t)&sb->sb_endzero - (caddr_t)&sb->sb_startzero);
 	sb->sb_timeo_nsecs = INFSLP;
 	mtx_leave(&sb->sb_mtx);
-	sounlock_shared(so);
 	sbunlock(sb);
 
 	if (pr->pr_flags & PR_RIGHTS && pr->pr_domain->dom_dispose)