TL/MLX5/MCAST: adding ip over ib mcast helper functions as well as some of the environment variables

[MamziB]

TL/MLX5: adding ip over ib mcast helper functions as well as some of the environment variables

[samnordmann]

It looks good to me. I just left some minor comments

[MamziB]

@samnordmann thanks for the comments. I have updated the commit.

[MamziB]

@samnordmann @Sergei-Lebedev Thank you guys for the helpful comments. I updated the commit and responded to the comments. Thank you.

[MamziB]

@Sergei-Lebedev @samnordmann thanks for the review. The commit is ready.
Thanks, Mamzi

[MamziB]

@samnordmann I can print a warning if fclose() fail. It will not affect the mcast init if it fclose() fails. Furthermore, other parts of UCC also do not check the return value. I will update the commit.

[MamziB]

@samnordmann I updated the commit.
Thank you. Mamzi

[samnordmann]

@samnordmann I can print a warning if fclose() fail. It will not affect the mcast init if it fclose() fails. Furthermore, other parts of UCC also do not check the return value. I will update the commit.

There could be an error also at file opening, and in this case it will affect the mcast init

[MamziB]

@samnordmann fopen() checks for error, if return is NULL, we are handling it

[MamziB]

@samnordmann I updated the commit, and I used the same return code as when we cannot open the file for fclose().

[Sergei-Lebedev]

@MamziB I will merge this PR once CI is back to normal, i.e. need to merge this #877 first