RDMA/core: Simplify roce_resolve_route_from_path()

Currently RoCE route resolve functionality is split between two
functions. (a) roce_resolve_route_from_path() and its helper function
rdma_resolve_ip_route().

Due to this multiple sockaddr src structures are created in both functions
with rdma_dev_addr is an interface between the two for checks.

Since there is only one user of rdma_resolve_ip_route() as RoCE, combine
the functionality of both functions to roce_resolve_route_from_path() and
further reduce the scope of rdma_dev_addr to core/addr.c

This also allow to extend addr_resolve() in subsequent patch to consider
netdev properties of GID in safer way under rcu lock.

Additionally src and dst addresses were always provided, so skip the src
addr NULL pointer check as they are present on the stack now.

Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>