RDMA/hfi1: Defer setting VL15 credits to link-up interrupt

RDMA/hfi1: Defer setting VL15 credits to link-up interrupt

Keep VL15 credits at 0 during LNI, before link-up. Store
VL15 credits value during verify cap interrupt and set
in after link-up. This addresses an issue where VL15 MAD
packets could be sent by one side of the link before
the other side is ready to receive them.

Reviewed-by: Mike Marciniszyn <[email protected]>
Reviewed-by: Dean Luick <[email protected]>
Reviewed-by: Dennis Dalessandro <[email protected]>
Signed-off-by: Jakub Byczkowski <[email protected]>
Signed-off-by: Dennis Dalessandro <[email protected]>
Signed-off-by: Doug Ledford <[email protected]>