pycsp: Implement Python binding for csp_sfp_send

The function sets internal flags on csp_conn_t that are not accessible in
Python, making it hard to implement in Python.

src/bindings/python/pycsp.c

@@ -255,6 +255,32 @@ static PyObject* pycsp_send(PyObject *self, PyObject *args) {
     Py_RETURN_NONE;
 }
 
+static PyObject* pycsp_sfp_send(PyObject *self, PyObject *args) {
+    PyObject* conn_capsule;
+    Py_buffer data;
+    uint32_t mtu;
+    uint32_t timeout;
+    if (!PyArg_ParseTuple(args, "Ow*II", &conn_capsule, &data, &mtu, &timeout)) {
+        return NULL; // TypeError is thrown
+    }
+
+    csp_conn_t* conn = get_obj_as_conn(conn_capsule, false);
+    if (conn == NULL) {
+        PyBuffer_Release(&data);
+        return NULL;
+    }
+
+    int res;
+    Py_BEGIN_ALLOW_THREADS;
+    res = csp_sfp_send(conn, data.buf, data.len, mtu, timeout);
+    Py_END_ALLOW_THREADS;
+
+    PyBuffer_Release(&data);
+    return res == CSP_ERR_NONE
+        ? Py_None
+        : PyErr_Error("csp_sfp_send()", res);
+}
+
 static PyObject* pycsp_transaction(PyObject *self, PyObject *args) {
     uint8_t prio;
     uint8_t dest;
@@ -1013,6 +1039,7 @@ static PyMethodDef methods[] = {
     {"accept",              pycsp_accept,              METH_VARARGS, ""},
     {"read",                pycsp_read,                METH_VARARGS, ""},
     {"send",                pycsp_send,                METH_VARARGS, ""},
+    {"sfp_send",            pycsp_sfp_send,            METH_VARARGS, ""},
     {"transaction",         pycsp_transaction,         METH_VARARGS, ""},
     {"sendto_reply",        pycsp_sendto_reply,        METH_VARARGS, ""},
     {"sendto",              pycsp_sendto,              METH_VARARGS, ""},