Handle pcapng version 1.2.

Handle pcapng version 1.2.

Some programs wrote it, even though the only "difference" is that some
new sysdig block types were added.  Any program that can read version
1.2 and its new block types should be able to read 1.0 files with the
same block types, so that wasn't a reason to bump the minor version
number.

(cherry picked from commit 1e0e97eb443874b8286547d39bf88af82d3312c7)