netdevice.h: fix kernel-doc warning

Fix kernel-doc warning in <linux/netdevice.h> (missing ':'):

..//include/linux/netdevice.h:1904: warning: No description found for parameter 'prio_tc_map[TC_BITMASK + 1]'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: David S. Miller <davem@davemloft.net>