fix usrsock remote_disconnect fail:
nsh> usrsocktest
...
Testing group "remote_disconnect" =>
[TEST ASSERT FAILED!]
In function "receive":
line 497: Assertion `(ssize_t)((ret)) == (ssize_t)((0))' failed.
got value: -1
should be: 0
Group "remote_disconnect": [FAILED]
...
Reference:
RECV(2)
NAME
recv, recvfrom, recvmsg - receive a message from a socket
...
RETURN VALUE
...
When a stream socket peer has performed an orderly shutdown,
the return value will be 0 (the traditional "end-of-file" return).
Datagram sockets in various domains (e.g., the UNIX and Internet domains)
permit zero-length datagrams. When such a datagram is received, the return value is 0.
Signed-off-by: chao an <anchao@xiaomi.com>