net: Make poll in InterruptibleRecv only filter for POLLIN events.

poll should block until there is data to be read or the timeout expires.

Filtering for the POLLOUT event causes poll to return immediately which leads to high CPU usage when trying to connect to non-responding peers through tor.

Removing POLLOUT matches how select is used when USE_POLL isn't defined.

src/netbase.cpp

@@ -347,7 +347,7 @@ static IntrRecvError InterruptibleRecv(uint8_t* data, size_t len, int timeout, c
 #ifdef USE_POLL
                 struct pollfd pollfd = {};
                 pollfd.fd = hSocket;
-                pollfd.events = POLLIN | POLLOUT;
+                pollfd.events = POLLIN;
                 int nRet = poll(&pollfd, 1, timeout_ms);
 #else
                 struct timeval tval = MillisToTimeval(timeout_ms);