Fix zdb_dump_block on little endian systems
When dumping a block on a little endian system the data must be
byte swapped to display correctly. Example incorrect output:
$ echo 0123456789abcdef > aaa
$ zdb -eR pp 3:1ee00:200
3:1ee00:200
0 1 2 3 4 5 6 7 8 9 a b c d e f 0123456789abcdef
000000: 3736353433323130 6665646362613938 0123456789abcdef
000010: 000000000000000a 0000000000000000 ................
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #4020