attribute: Avoid shifting 32 bit integers.

attribute: Avoid shifting 32 bit integers.

att_logical_or() is called from com_check() to set up a bitmask where
a bit is set if and only if it corresponds to an existing attribute.
Doing "1 << i" is wrong in this context because the constant "1" is a
(signed) 32 bit quantity and we need to be able to shift by more than
31 bits for the attribute mask.

Fix this by using an uint64_t variable instead.