cifs: add pid of initiating process to spnego upcall info

This will allow the upcall to poke in /proc/<pid>/environ and get
the value of the $KRB5CCNAME env var for the process.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>