pfsync: Remove a redundant assignment of if_type

On initializing the interface, if_alloc(IFT_PFSYNC) has set if_type
already.

No functional change intended.

MFC after: 1 week

(cherry picked from commit 48af70e7c82150942fd095a38131e454e47ad162)
(cherry picked from commit 082a6da890f3487f1465c0757784798ebe38ef84)