Check port number supplied by user verbs cmds in ibcore.

The ib_uverbs_create_ah() ind ib_uverbs_modify_qp() calls receive
the port number from user input as part of its attributes and assumes
it is valid. Down on the stack, that parameter is used to access kernel
data structures. If the value is invalid, the kernel accesses memory
it should not. To prevent this, verify the port number before using it.

Linux commit:
5ecce4c9b17bed4dc9cb58bfb10447307569b77b
a62ab66b13a0f9bcb17b7b761f6670941ed5cd62
5a7a88f1b488e4ee49eb3d5b82612d4d9ffdf2c3

MFC after: 1 week
Sponsored by: Mellanox Technologies