ibcore: Introduce ib_port_phys_state enum.

In order to improve readability, add ib_port_phys_state enum to replace
the use of magic numbers.

Linux commit:
72a7720fca37fec0daf295923f17ac5d88a613e1

MFC after: 1 week
Reviewed by: kib
Sponsored by: Mellanox Technologies // NVIDIA Networking