shill: validate WPA passwords (at least on calls to GetService)

BUG=chromium-os:20897
TEST=unittests, some autotests

the following autotests now pass, at least in the wifi_vm_config:
- network_WiFiManager.000_SSID_Length_Limit
* network_WiFiManager.021CheckWPA_BadPassphraseLength
- network_WiFiSecMat.010CheckWPA_TKIP
- network_WiFiSecMat.011CheckWPA_AES
- network_WiFiSecMat.012CheckWPA_Multi
- network_WiFiSecMat.018CheckWPA_CounterMeasures

'*' denotes a newly passing test

Change-Id: I7296c0c0f6a8509b488aee573d5ab14d7a2fc235
Reviewed-on: http://gerrit.chromium.org/gerrit/8666
Reviewed-by: Paul Stewart <pstew@chromium.org>
Reviewed-by: Chris Masone <cmasone@chromium.org>
Tested-by: mukesh agrawal <quiche@chromium.org>
diff --git a/ieee80211.h b/ieee80211.h
index 5fa34bd..bec681f 100644
--- a/ieee80211.h
+++ b/ieee80211.h
@@ -14,6 +14,10 @@
 const unsigned int kWEP40HexLen = 10;
 const unsigned int kWEP104AsciiLen = 13;
 const unsigned int kWEP104HexLen = 26;
+
+const unsigned int kWPAAsciiMinLen = 8;
+const unsigned int kWPAAsciiMaxLen = 63;
+const unsigned int kWPAHexLen = 64;
 };
 
 }  // namespace shill