Added check for Infiniband PCIe link width and speed.

[yqin]

This PR should address the difference between what PCI-e link layer reports and driver reports.

[Obihoernchen]

Works very well!

[kcgthb]

It works very well for HCAs using the mlx5_core module, indeed.

But AFAICT, mlx4_ib doesn't provide the /sys/class/infiniband/<device>/device/current_link_{speed,width} files, which make the check fail:

# nhc -d -e 'check_hw_ib 56'
DEBUG:  Debugging activated via -d option.
DEBUG:  Evaluating single check line:  check_hw_ib 56
[...]
/etc/nhc/scripts/lbnl_hw.nhc: line 134: /sys/class/infiniband/mlx4_0/device/current_link_speed: No such file or directory
/etc/nhc/scripts/lbnl_hw.nhc: line 137: /sys/class/infiniband/mlx4_0/device/current_link_width: No such file or directory
[1617908392] - DEBUG:  Found ACTIVE (LinkUp) IB Port mlx4_0:1 (56 Gb/sec) with PCI-e link 56x 56 GT/s

This is with a ConnectX-3 card: "Mellanox Technologies MT27500 Family [ConnectX-3]"

[mej]

This looks great; thanks, Yong!

I will address @kcgthb's comments by checking for the existence of the file prior to merge. So thanks to you both! 😃