[DPP] Add _GENERIC suffix to EASY_CONNECT_EVENT_FAILURE code

Following API council review, rename EASY_CONNECT_EVENT_FAILURE to
EASY_CONNECT_EVENT_FAILURE_GENERIC.

Bug: 122984877
Test: atest DppManagerTest
Change-Id: If1a9e634d0750695f779f192062066fced23b8cf
2 files changed