Add missing value_string for NM_EV_* introduced recently
Add missing value_string for NM_EV_* introduced recently

Fixes: 0277cddab2bb6b09f02e998c0aa9ff78d41c327c
Change-Id: I70266767d4f85e8c14ecf477af7fab0706698067

osmocom/osmo-bts,osmocom/osmo-bts,osmocom/osmo-bts