Xenial SRU V2 - NMI watchdog Bug and call traces when trinity is executed

[Tim Gardner]

Patch 0003-ext4-more-efficient-SEEK_DATA-implementation.patch as attached to the bug did not
apply cleanly, so I did my own backport. Clearly I got it wrong. This patch will actually
apply with a bit of fuzz, so that is V2. Test kernel at http://people.canonical.com/~rtg/ext4-lp1602524/
No changes to patches 1 or 2.

rtg

[PATCH 1/3 Xenial SRU V2] ext4: factor out determining of hole size
[PATCH 2/3 Xenial SRU V2] ext4: return hole from ext4_map_blocks()
[PATCH 3/3 Xenial SRU V2] ext4: more efficient SEEK_DATA implementation