ibcore: Always check return value from ib_init_ah_from_wc().

This prevents code from accepting RoCEv1 connections when
only ROCEv2 is enabled and vice versa.

Linux commit:
0c4386ec77cfcd0ccbdbe8c2e67dd3a49b2a4c7f

Submitted by: hselasky@
Approved by: hselasky (mentor)
MFC after: 1 week
Sponsored by: Mellanox Technologies