RDMA/rxe: Move rxe_init_av() to rxe_av.c

Move the function rxe_init_av() to rxe_av.c file and use it instead of
calling rxe_av_from_attr() and rxe_av_fill_ip_info(), also remove the
unused rxe_dev parameter from rxe_init_av().

Signed-off-by: Kamal Heib <kamalheib1@gmail.com>
Reviewed-by: Yuval Shaia <yuval.shaia@oracle.com>
Reviewed-by: Zhu Yanjun <yanjun.zhu@oracle.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>