cifs: remove some minor warnings pointed out by kernel test robot

Correct some trivial warnings caused when new file unc.c
was created. For example:

   In file included from fs/cifs/unc.c:11:
>> fs/cifs/cifsproto.h:44:28: warning: 'struct TCP_Server_Info' declared inside parameter list will not be visible outside of this definition or declaration
      44 | extern int smb_send(struct TCP_Server_Info *, struct smb_hdr *,
Reported-by: Nkernel test robot <lkp@intel.com>
Signed-off-by: NSteve French <stfrench@microsoft.com>

fs/cifs/unc.c

@@ -7,7 +7,11 @@
  *              Jeff Layton <jlayton@kernel.org>
  */
 
+#include <linux/fs.h>
 #include <linux/slab.h>
+#include <linux/inet.h>
+#include <linux/ctype.h>
+#include "cifsglob.h"
 #include "cifsproto.h"
 
 /* extract the host portion of the UNC string */