Prevent frag from being freed out from under us in the case
the PML callback routine calls usnic_free(). We accomplish this
by delaying decrement of sf_bytes_to_ack until after the callback is
performed, since sf_bytes_to_ack == 0 is condition of freeing the frag.
Fixes Cisco bug CSCuj45094.
Authored-by: Reese Faucette <rfaucett@cisco.com>
cmr=v1.7.3
This commit was SVN r29264.