npl/riot: simplify ble_npl_hw_is_in_critical()
npl/riot: simplify ble_npl_hw_is_in_critical()

Recently the RIOT IRQ API was extended to support irq_is_enabled(),
so time to switch away from the hacked implementation of
ble_npl_hw_is_in_critical().

apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble