eal/bsd: silence unsupported interrupts error

eal/bsd: silence unsupported interrupts error

Currently, nic_uio driver does not support interrupts, so any
attempts to install an interrupt handler will fail with a
not supported error, which will cause an error message that is
confusing to the user.

Silence this error by moving it to debug log level, and reword
the message to avoid containing the word "Error", to avoid
triggering DTS test failures [1].

[1] https://git.dpdk.org/tools/dts/tree/tests/TestSuite_scatter.py?#n110

Fixes: 23150bd8d8a8 ("eal/bsd: add interrupt thread")

Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>