Improved logging of gtaskqueue failues

Check the return code of intr_setaffinity() and log any errors
it returns. When a qid is not located, log an error before returning
failure. Also, use func rather than hardcoding the function name

Reviewed by: sbruno
Approved by: sbruno (mentor)
Sponsored by: Limelight Networks
Differential Revision: https://reviews.freebsd.org/D12436