adb: clean up handle_host_request.

Previously, we were returning the result of SendOkay/SendFail in a few
places after handling a host request, which is incorrect for two
reasons. First, the return type of SendOkay/SendFail is bool, and
handle_host_request was expected to return 0 on success. Second, we
don't care if the SendOkay fails; if we got to that point, we're done
with the request, regardless of whether we succeeded to report our
result. The result of this was a spurious failure result reported after
the initial result, which was ignored by the adb client.

Test: manually straced adb server
Test: python test_adb.py
Test: python test_device.py
Change-Id: I7d45ba527e1faccbbae5b15e7a0d1557b0a84858
diff --git a/adb/sockets.cpp b/adb/sockets.cpp
index 69b5180..1534792 100644
--- a/adb/sockets.cpp
+++ b/adb/sockets.cpp
@@ -685,13 +685,9 @@
     if (service) {
         asocket* s2;
 
-        /* some requests are handled immediately -- in that
-        ** case the handle_host_request() routine has sent
-        ** the OKAY or FAIL message and all we have to do
-        ** is clean up.
-        */
-        if (handle_host_request(service, type, serial, transport_id, s->peer->fd, s) == 0) {
-            /* XXX fail message? */
+        // Some requests are handled immediately -- in that case the handle_host_request() routine
+        // has sent the OKAY or FAIL message and all we have to do is clean up.
+        if (handle_host_request(service, type, serial, transport_id, s->peer->fd, s)) {
             D("SS(%d): handled host service '%s'", s->id, service);
             goto fail;
         }