vrf: add CRC32c offload to device features

vrf: add CRC32c offload to device features

SCTP sockets originated in a VRF can improve their performance if CRC32c
computation is delegated to underlying devices: update device features,
setting NETIF_F_SCTP_CRC. Iterating the following command in the topology
proposed with [1],

 # ip vrf exec vrf-h2 netperf -H 192.0.2.1 -t SCTP_STREAM -- -m 10K

the measured throughput in Mbit/s improved from 2395 ± 1% to 2720 ± 1%.

[1] https://www.spinics.net/lists/netdev/msg486007.html

Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Reviewed-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Acked-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>