conncheck: Don't lookup prflx pair for UDP candidates

Code comment mentions peer reflexive candidate pair should be selected
only in the case of TCP local candidates, but it was done in all cases.
7 jobs for sfb-prflx in 5 minutes and 24 seconds
Status Job ID Name Coverage
  Build
passed #325254
build autotools

00:00:59

passed #325255
build meson

00:00:29

 
  Test
passed #325257
distcheck autotools

00:02:45

passed #325259
doc-and-install meson

00:00:45

passed #325293
test autotools

00:01:40

passed #325258
allowed to fail
test meson

00:00:47

failed #325256
test autotools

00:01:40