Ignore ESHUTDOWN on the server side too

We got the client, but not the server.  We can see the same error there
too.

Change-Id: I24058efedc8f4d09518f905ac9582ad37ef031e7
diff --git a/aos/network/sctp_server.cc b/aos/network/sctp_server.cc
index 6e32c8a..c8563d5 100644
--- a/aos/network/sctp_server.cc
+++ b/aos/network/sctp_server.cc
@@ -116,7 +116,7 @@
   // And send.
   const ssize_t size = sendmsg(fd_, &outmsg, MSG_NOSIGNAL | MSG_DONTWAIT);
   if (size == -1) {
-    if (errno == EPIPE || errno == EAGAIN) {
+    if (errno == EPIPE || errno == EAGAIN || errno == ESHUTDOWN) {
       return false;
     }
     PCHECK(size == static_cast<ssize_t>(data.size()));