net: dns: Check that dispatcher table is not overflowing

Add CHECKIF() checks that verify that dispatcher table is
not overflowing.

Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>
(cherry picked from commit 2ff26674a26d544df7a54b9481ec4d7b1430d47b)
1 file changed