gve: Make LRO work for jumbo packets

Each Rx descriptor points to a packet buffer of size 2K, which means
that MTUs greater than 2K see multi-descriptor packets. The TCP-hood of
such packets was being incorrectly determined by looking for a flag on
the last descriptor instead of the first descriptor.

Also fixed and progressed the version number.

Reviewed by: markj
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D41754

(cherry picked from commit 5f62584a9adb7887bae33af617cfa4f43017abf8)