netmap_do_regif: Reverse error path vs normal path
netmap_do_regif: Reverse error path vs normal path

The error exit path should reverse all operations in backward order of
the normal path. Till this commit if netmap_mem_if_new fails then
netmap_krings_put won't be called and the usage count will leak.

luigirizzo/netmap,luigirizzo/netmap,luigirizzo/netmap,luigirizzo/netmap,luigirizzo/netmap