misc: fix alignment warnings on ARM

misc: fix alignment warnings on ARM

Some temporary char buffers allocated on the stack are not properly
aligned when typecast to a structure containing __u32 or __u64 types,
and this can cause alignment warnings on ARM and other alignment
sensitive architectures, and potential slowdowns to do fixups.

Fix the buffer alignment to avoid such issues.

Addresses: https://bugzilla.redhat.com/show_bug.cgi?id=680090

Reported-by: Gordan Bobic <gordan.bobic@gmail.com>
Signed-off-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>