igb: Drop unnecessary checks in transmit path

igb: Drop unnecessary checks in transmit path

BugLink: http://bugs.launchpad.net/bugs/1547674
This patch drops several checks that we dropped from ixgbe some ago.  It
should not be possible for us to be called with either of the conditional
statements returning true so we can just drop them from the hot-path.

Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
(cherry picked from net-next commit 9c2f186e45faa34d5f6ff52aa84c361d4be72288)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>