CIFS: Expand CurrentMid field

While in CIFS/SMB we have 16 bit mid, in SMB2 it is 64 bit.
Convert the existing field to 64 bit and mask off higher bits
for CIFS/SMB.

Signed-off-by: Pavel Shilovsky <piastry@etersoft.ru>

diff --cc fs/cifs/cifsglob.h
Simple merge

diff --cc fs/cifs/cifsproto.h
Simple merge

diff --cc fs/cifs/misc.c
Simple merge