[CIFS] clean up server protocol handling

We're currently declaring both a sockaddr_in and sockaddr6_in on the
stack, but we really only need storage for one of them. Declare a
sockaddr struct and cast it to the proper type. Also, eliminate the
protocolType field in the TCP_Server_Info struct. It's redundant since
we have a sa_family field in the sockaddr anyway.

We may need to revisit this if SCTP is ever implemented, but for now
this will simplify the code.

CIFS over IPv6 also has a number of problems currently. This fixes all
of them that I found. Eventually, it would be nice to move more of the
code to be protocol independent, but this is a start.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>