Handle incoming packets that don't fit into the receive buffer.

Handle incoming packets that don't fit into the receive buffer.

If the receive buffer size is reduced while there are still incoming
packets in flight, it can be that those will not fit inside the receive
buffer. Instead of calling abort(), just handle as much of the packet as
we can fit in the receive buffer, or handle the whole packet if it is in
order since we bypass the receive buffer in that case.