learning-switch: Avoid violating C aliasing rules initializing actions.

learning-switch: Avoid violating C aliasing rules initializing actions.

The C standard says that an object that is declared of one particular type
must not be accessed through a pointer to another type, with a few notable
exceptions.  This code was violating those rules, and GCC 4.4 complains
about it.  This commit fixes the problem by using one of the exceptions:
it's always OK to access an object as an array of character type (which is
what memcpy() does implicitly).

Reported-by: Justin Pettit <jpettit@nicira.com>