The libpcap callback "user" argument *should* have been a "void *", as

The libpcap callback "user" argument *should* have been a "void *", as
it's a pointer to an arbitrary object, assumed to be correctly aligned,
not a pointer to a not-necessarily-properly-aligned array of bytes.
Cast it, so we won't get alignment warnings.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@21940 f5534014-38df-0310-8fa8-9805f1628bb7