We don't need it anymore. Note, the modification of both socket buffers
is serialized.

Index: sys/kern/uipc_socket2.c
===================================================================
RCS file: /cvs/src/sys/kern/uipc_socket2.c,v
diff -u -p -r1.180 uipc_socket2.c
--- sys/kern/uipc_socket2.c	17 Feb 2025 08:56:33 -0000	1.180
+++ sys/kern/uipc_socket2.c	17 Feb 2025 09:34:24 -0000
@@ -609,8 +609,6 @@ sowakeup(struct socket *so, struct sockb
 int
 soreserve(struct socket *so, u_long sndcc, u_long rcvcc)
 {
-	soassertlocked(so);
-
 	mtx_enter(&so->so_rcv.sb_mtx);
 	mtx_enter(&so->so_snd.sb_mtx);
 	if (sbreserve(&so->so_snd, sndcc))