modules: hal_norfic: rise 802.15.4 NET core init priority

Due to internal dependencies on other modules init priority
the 802.15.4 priority level must be increased. Former init
priority caused the module to be initialied before those
it depends on, so that lead to hard faults.

Signed-off-by: Piotr Pryga <piotr.pryga@nordicsemi.no>