another set of ppc405_enet changes

I wanted to limit this patch to be just a rework of the static var's but I
ended up changing more things. I will attempt a summary of the changes.
I did not compile/fix the stuff ifdef'd out by default.

I attached the output from some runs with nttcp before and after the changes.
It does not appear like there is any noticable change in performace from these
changes. "-u" is for UDP "-r" is Rx'd on the 405GP Tx'd by my x86 box, "-t" is
Tx'd by the 405GP Rx'd by the x86.
One thing to look into would be the diff between UDP tx packets to the
number rx'd on the other side. I don't know where the packets are being dropped
now.

Config.ini changed to CONFIG_PPC405_ENET to be tristate instead of just bool.

Change NUM_RX to 32 and NUM_TX to 8. Doesn't change performace noticablely.
Moved probe1 code into init function.

kfree of private struct on module unload or failure to register netdevice.

Used skb->len instead of tail-head in places.

For both tx/rx eob int's clear reg first then loop through, instead of loop
clear, goto top of loop again.

Moved tx stat counts into tx eob from hard_xmit. In tx_eob moved netif_wake
outside of loop.

In rx_eob wait untill end of function to refill slots instead of after
each packet. Also did skb_put instead of += tail and len. Put in check
for dev_alloc_skb failure but still no recovery when OOM.

Orig--------------------
# ./nttcp-ppc -T  -u -r -n 100000 192.168.1.5
     Bytes  Real s   CPU s Real-MBit/s  CPU-MBit/s   Calls  Real-C/s   CPU-C/s
l409600000   36.75   24.11     89.1642    135.9104  100001   2721.10    4147.7
1409600000   36.75    3.10     89.1754   1057.0323  100003   2721.50   32259.0
# ./nttcp-ppc -T  -u -t -n 100000 192.168.1.5
     Bytes  Real s   CPU s Real-MBit/s  CPU-MBit/s   Calls  Real-C/s   CPU-C/s
l409600000   34.81   22.75     94.1400    144.0352  100003   2873.01    4395.7
1388304896   34.81    1.54     89.2353   2017.1683   94802   2723.27   61559.7
# ./nttcp-ppc -T   -t -n 100000 192.168.1.5
     Bytes  Real s   CPU s Real-MBit/s  CPU-MBit/s   Calls  Real-C/s   CPU-C/s
l409600000   46.71   44.44     70.1553     73.7354  100000   2140.97    2250.2
1409600000   46.71    6.79     70.1555    482.5920  288192   6170.12   42443.6
# ./nttcp-ppc -T   -r -n 100000 192.168.1.5
     Bytes  Real s   CPU s Real-MBit/s  CPU-MBit/s   Calls  Real-C/s   CPU-C/s
l409600000   44.21   42.45     74.1172     77.1920  100161   2265.52    2359.5
1409600000   44.21    2.01     74.1199   1630.2488  100000   2261.96   49751.2

With Patch--------------------

# ./nttcp-ppc -T -u -r -n 100000 192.168.1.5
     Bytes  Real s   CPU s Real-MBit/s  CPU-MBit/s   Calls  Real-C/s   CPU-C/s
l409600000   36.39   24.43     90.0534    134.1302  100001   2748.24    4093.4
1409600000   36.38    3.19     90.0617   1027.2100  100003   2748.55   31348.9
# ./nttcp-ppc -T -u -r -n 100000 192.168.1.5
     Bytes  Real s   CPU s Real-MBit/s  CPU-MBit/s   Calls  Real-C/s   CPU-C/s
l409600000   36.33   24.14     90.1953    135.7415  100001   2752.57    4142.5
1409600000   36.32    3.34     90.2083    981.0778  100003   2753.02   29941.0
# ./nttcp-ppc -T -u -t -n 100000 192.168.1.5
     Bytes  Real s   CPU s Real-MBit/s  CPU-MBit/s   Calls  Real-C/s   CPU-C/s
l409600000   34.81   20.59     94.1261    159.1452  100003   2872.59    4856.9
1386686976   34.82    1.77     88.8523   1747.7377   94407   2711.58   53337.3
# ./nttcp-ppc -T -t -n 100000 192.168.1.5
     Bytes  Real s   CPU s Real-MBit/s  CPU-MBit/s   Calls  Real-C/s   CPU-C/s
l409600000   46.22   41.92     70.8989     78.1679  100000   2163.66    2385.5
1409600000   46.22    6.35     70.8987    516.0315  287353   6217.33   45252.4
# ./nttcp-ppc -T -r -n 100000 192.168.1.5
     Bytes  Real s   CPU s Real-MBit/s  CPU-MBit/s   Calls  Real-C/s   CPU-C/s
l409600000   44.79   42.63     73.1577     76.8661  100099   2234.81    2348.1
1409600000   44.79    2.80     73.1578   1170.2857  100000   2232.60   35714.3