net: Eliminate duplicated codes by creating one new function in_dev_select_addr

There are two duplicated loops codes which used to select right
address in current codes. Now eliminate these codes by creating
one new function in_dev_select_addr.

Signed-off-by: Gao Feng <fgao@ikuai8.com>
Signed-off-by: David S. Miller <davem@davemloft.net>