net: move the ptype_all and ptype_base declarations to include/linux/netdevice.h

ptype_all and ptype_base are declared in net/core/dev.c as non-static,
because they are used by net-procfs.c too. However, a "make W=1" build
complains that there was no previous declaration of ptype_all and
ptype_base in a header file, so this way of declaring things constitutes
a violation of coding style.

Let's move the extern declarations of ptype_all and ptype_base to the
linux/netdevice.h file, which is included by net-procfs.c too.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>