Starting LBA is a 64bit number, so use htole64 instead of htole32. The
latter casts the LBA to a 32-bit number before assigning it to the 64
bit structure entity. This works fine on the first 2TB of TRIMs, but
terrible beyond that due to trucation.

Also, add an assert to make sure we don't end too many DSM TRIM
entries in one request.

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