sys/vfs/hammer: Use bitwise OR to generate ondisk localization

sys/vfs/hammer: Use bitwise OR to generate ondisk localization

Use |= to generate localization field for B-Tree elements and
cursor keys instead of +=, since lower 16 bits are bitfields
(or safer to treat INODE=0x1 and MISC=0x2 as bitfields).

The typical code to generate ondisk localization value is to
do either of the followings.

  ondisk_lo = local_variable          + {INODE or MISC};
  ondisk_lo = ip->obj_localization    + {INODE or MISC};
  ondisk_lo = HAMMER_XXX_LOCALIZATION + {INODE or MISC};
              ^^^^^^^^^^^^^^^^^^^^^^^   ^^^^^^^^^^^^^^^
              (A)32 bits localization   (B)lower 16 bits
                 with usually 0 for
                 lower 16 bits for type

Adding (A) and (B) to synthesize PFS id and localization type
could lead to a potential bug if (A) already has type bits set
to either INODE or MISC. For example if (A) had INODE for type
bits and the code is to += INODE for (B), then type bits turn
into MISC (1+1=2) which is not the intention of the code.

This could potentially occur with the first example of above
three where (A) is a local variable or a function argument.
It is not too obvious from the code whether that local variable
has 0 for the lower 16 bits (which basically should be).
If the code just always uses |= no such thing will happen.