[PATCH net-next] pktgen: Upstreaming features useful for xen-netback/front testing

This series is my work during stressing the xen network drivers, hopefully
others can benefit from it.
1/3: Filling payload with pattern, useful for checking data correctness when the
packets travelling without checksum (~ intrahost VM-to-VM). Already sent it
separately
2/3: fine-grained buffer geometrics
3/3: sending TCP GSO packets. This is an RFC yet, as I'm not certain about all
things changed here

Signed-off-by: Zoltan Kiss <redacted>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Thomas Graf <tgraf@suug.ch>
Cc: Joe Perches <joe@perches.com>
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: xen-devel@lists.xenproject.org