net: ip: Add protocol family type to conn handler

As we are adding more protocol families and protocol types
to connection handlers, some values might be same across
different types. Current connection handler only stores
proto type to match the handler, which is not enough if
we add more types. Also combination of family and types
may vary too. So adding family to connection handler to
figure out best match.

Also changing proto variable in net_conn from u8_t to u16_t.
net_context has 16 bit proto.

Signed-off-by: Ravi kumar Veeramally <ravikumar.veeramally@linux.intel.com>