iavf: rare bus error when creating interface

[vrpolakatcisco]

In rls2502 we executed many AVF tests, this is after migrating CSIT to use plugins/dev_iavf instead of the previous plugins/avf. Most tests have no issues, but I have spotted one run (so far) where dev_attach failed [0]: Retval nonzero in object {'_0': 57, 'context': 31111748, 'dev_index': 4294967295, 'retval': -5, 'error_string': 'bus error'}

The context value is suspiciously high, but normal execution does not log it, so special verify runs are needed, although they are not likely to reproduce the bus error due to its low frequency.

[0] https://s3-logs.fd.io/vex-yul-rot-jenkins-1/csit-vpp-perf-report-iterative-2502-2n-icx/45/log.html.gz#s1-s1-s1-s5-s20-t3-k2-k6-k1-k1-k1-k1-k1-k13-k1-k1-k1-k1