p2p: Fall back to blocking sockets if the async connection fails

p2p: Fall back to blocking sockets if the async connection fails

Due to a kernel bug, trying to connect through a non blocking socket
may fail and return POLLHUP. In that case the connection procedure falls
back to using blocking sockets and this needs to be delayed until the
kernel sends a DM to the peer.
This is slightly hackish but this code path should get obsolete once
neard runs on top of 3.10 or later kernels.