compat: fix compile errors when assembly is built into modules

On powerpc, modules can be compiled and linked with an assembly file, adding
missing symbols that the compiler references when using -Os.

== ckmake-report.log ==

1   2.6.24              [  OK  ]
2   2.6.25              [  OK  ]
3   2.6.26              [  OK  ]
4   2.6.27              [  OK  ]
5   2.6.28              [  OK  ]
6   2.6.29              [  OK  ]
7   2.6.30              [  OK  ]
8   2.6.31              [  OK  ]
9   2.6.32              [  OK  ]
10  2.6.33              [  OK  ]
11  2.6.34              [  OK  ]
12  2.6.35              [  OK  ]
13  2.6.36              [  OK  ]
14  2.6.37              [  OK  ]
15  2.6.38              [  OK  ]
16  2.6.39              [  OK  ]
17  3.0.50              [  OK  ]
18  3.1.10              [  OK  ]
19  3.2.33              [  OK  ]
20  3.3.8               [  OK  ]
21  3.4.17              [  OK  ]
22  3.5.7               [  OK  ]
23  3.6.5               [  OK  ]
24  3.7.0               [  OK  ]

real    0m33.803s
user    11m24.519s
sys     3m39.690s

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
compat: do not access default_ethtool_ops

&default_ethtool_ops is not exported in kernel 3.7.4 and earlier and it
should be be accessed from compat.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
compat: update kernel versions in bin/get-compat-kernels

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>