Add detail to sctp CHECK statements

Add a suggestion to help point users in a somewhat more helpful
direction.

Change-Id: I35f5d1ccd21d475c98d02a3ada2e1e618e060a41
Signed-off-by: James Kuszmaul <jabukuszmaul+collab@gmail.com>
diff --git a/aos/network/sctp_client.h b/aos/network/sctp_client.h
index 806026c..bc3d1f6 100644
--- a/aos/network/sctp_client.h
+++ b/aos/network/sctp_client.h
@@ -49,8 +49,12 @@
     // one full sized packet in flight.
     max_size = max_size * 10;
 
-    CHECK_GE(ReadRMemMax(), max_size);
-    CHECK_GE(ReadWMemMax(), max_size);
+    CHECK_GE(ReadRMemMax(), max_size)
+        << "rmem_max is too low. To increase rmem_max temporarily, do sysctl "
+           "-w net.core.rmem_max=NEW_SIZE";
+    CHECK_GE(ReadWMemMax(), max_size)
+        << "wmem_max is too low. To increase wmem_max temporarily, do sysctl "
+           "-w net.core.wmem_max=NEW_SIZE";
     PCHECK(setsockopt(fd_, SOL_SOCKET, SO_RCVBUF, &max_size,
                       sizeof(max_size)) == 0);
     PCHECK(setsockopt(fd_, SOL_SOCKET, SO_SNDBUF, &max_size,