UPF_Tests: adjust to rename 'endecaps' to 'tunend'

osmo-upf has changed the naming of GTP action kinds, need to adjust the
test here to avoid failing tests.

Related: I49ac7b1f8b5b74f586edfed1dfb29f9af55a521b (osmo-upf)
Change-Id: I6fe4a4cf02ca05b772491d11a5edbdbd7b0b429a
1 file changed