fm10k: fold fm10k_pull_tail into fm10k_add_rx_frag

This change folds the fm10k_pull_tail call into fm10k_add_rx_frag.  The
advantage to doing this is that the fragment doesn't have to be modified
after it is added to the skb.

Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
Tested-by: Krishneil Singh <Krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>