ibcore: Block processing of alternate path handling in RoCE RX CM messages.

Due to the below reasons, it is better to not support alternate path receive
messages for RoCE in near term.

1. Alternate path for RoCE is not supported at rdmacm layer.
2. It is not supported in uverbs/core layer for RoCE.
3. Alternate path for IPv6 for link local address cannot resolve route

determinstically without a valid incoming interface ID whose usecase
make sense only with dual port mode.

4. init_av_from_path while processing LAP messages for IB and RoCE can

lead to adding duplicate entry of AV into the port list, leads to list
corruption.

5. rdma-core userspace a well known userspace implementation has removed

support of libucm which use ucm.ko module, which is the only module that
can trigger alternate path related messages.

6. ucm kernel module is requested to be removed from the IB core in

the following patch, https://patchwork.kernel.org/patch/10268503/ .

Linux commit:
97c45c2c28cd291e06778d9d36a0f60ee74726bc

Reviewed by: kib
Sponsored by: Mellanox Technologies // NVIDIA Networking

(cherry picked from commit 0f2e5b432dcdd19955285169f1603473219ac130)