MINOR: stream-int: Notify caller when an error is reported after a rcv_buf()

For the same reason than for the commit b46784b1c ("MINOR: stream-int: Notify
caller when an error is reported after a rcv_pipe()"), we return 1 after the
call to rcv_buf() in si_cs_send() to notify the caller some processing may be
triggered.

This patch is not flagged as a bug because no strange behaviour was yet observed
without it. It is just a proactive fix to be consistent.
1 file changed