shill: cellular_capability_universal: retry apns on any error

modemmanager1 never returns kInvalidApn errors.  modemmanager1 should
be fixed so that it will, but it is not going to happen until we get a
firmware upgrade of the E362 modem.  Work around that by treating all
connect errors as retryable on E362 modems.

BUG=chromium-os:30631
TEST=unit tests and connect to verizon LTE
Change-Id: I74e5b581f6c04c9c832afc2d56a8df9a53b0e6e7
Reviewed-on: https://gerrit.chromium.org/gerrit/22061
Reviewed-by: Gary Morain <gmorain@chromium.org>
Tested-by: Jason Glasgow <jglasgow@chromium.org>
Commit-Ready: Jason Glasgow <jglasgow@chromium.org>
diff --git a/cellular_service.h b/cellular_service.h
index 75d7dc1..f2e133a 100644
--- a/cellular_service.h
+++ b/cellular_service.h
@@ -98,8 +98,8 @@
 
   Stringmap *GetUserSpecifiedApn();
   Stringmap *GetLastGoodApn();
-  void SetLastGoodApn(const Stringmap &apn_info);
-  void ClearLastGoodApn();
+  virtual void SetLastGoodApn(const Stringmap &apn_info);
+  virtual void ClearLastGoodApn();
 
  private:
   friend class CellularServiceTest;