Index: uipc_mbuf.c
===================================================================
RCS file: /cvs/src/sys/kern/uipc_mbuf.c,v
retrieving revision 1.253
diff -u -p -r1.253 uipc_mbuf.c
--- uipc_mbuf.c	16 Jan 2018 19:44:34 -0000	1.253
+++ uipc_mbuf.c	9 Mar 2018 01:34:05 -0000
@@ -812,11 +812,12 @@ m_adj(struct mbuf *mp, int req_len)
 		while (m != NULL && len > 0) {
 			if (m->m_len <= len) {
 				len -= m->m_len;
+				m->m_data += m->m_len; /* move alignment */
 				m->m_len = 0;
 				m = m->m_next;
 			} else {
-				m->m_len -= len;
 				m->m_data += len;
+				m->m_len -= len;
 				len = 0;
 			}
 		}