IB/ipoib: Make ipoib_intercept_dev_id_attr() static

The function ipoib_intercept_dev_id_attr() is only used in ipoib_main.c

Fixes: f6350da4

 ("IB/ipoib: Log sysfs 'dev_id' accesses from userspace")
Signed-off-by: Kamal Heib <kamalheib1@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>