conn->sendsize is used in rpmsg_socket_ept_cb() and
rpmsg_socket_connect_internal(), the connected event may be missed
as stated below:
1. in rpmsg_socket_connect_internal(), judge conn->sendsize == 0
and prepare to wait sendsem;
2. interrupt by rptun thread, rpmsg_socket_ept_cb() is called to
update conn->sendsize and post the sendsem, but the no one wait
rx sem yet, so not post (see rpmsg_socket_post());
3. return to rpmsg_socket_connect_internal() to wait the sendsem, but
has miss the connected event.
So add recvlock in rpmsg_socket_connect_internal() also.
Signed-off-by: Bowen Wang <wangbowen6@xiaomi.com>