Return ret in op_ifentry(..) to mute a -Wunused-but-set-variable
warning

This should also now undetected error conditions with
value->var.subs[sub - 1] == LEAF_ifPhysAddress where string_get(..)
could fail if iifp->physaddr and/or iifp->physaddrlen were deemed
invalid.

Reported by: Jenkins (clang job) [1], Jenkins (gcc 4.9 job) [2]
Sponsored by: EMC / Isilon Storage Division