intrng: Releasing interrupt source should clear interrupt table full state.

The first release of an interrupt in a situation where the interrupt table
is full should schedule a full table check the next time an interrupt is
allocated. A full check is necessary to ensure maximum separation between
the order of allocation and the order of release.

Submitted by: ehem_freebsd@m5p.com (initial version)
Discussed in: https://reviews.freebsd.org/D29310
MFC after: 4 weeks