RTL8139 driver malfunctions on real HW

Overall experience is that it behaves fine at startup but gets slower and slower every minute. Stuff like ping still works fine, but for example more complex stuff like FF with facebook.com starts to render unuseable very fast and ends with incomplete loaded websites. Chatzilla does not send any of my writings after a few minutes, but I still get answers for a while longer. The funny aspect is that this lagging behavior takes over on all over devices in my home network. Wireshark does not say anything useable though. Log shows loading of FF and using it for chatting and facebook. rtl8139 was debug enabled in all components.