ip xfrm: support setting XFRMA_SET_MARK_MASK attribute in states

ip xfrm: support setting XFRMA_SET_MARK_MASK attribute in states

The XFRMA_SET_MARK_MASK attribute can be set in states (4.19+)
It is optional and the kernel default is 0xffffffff
It is the mask of XFRMA_SET_MARK(a.k.a. XFRMA_OUTPUT_MARK in 4.18)

e.g.
./ip/ip xfrm state add output-mark 0x6 mask 0xab proto esp \
 auth digest_null 0 enc cipher_null ''
ip xfrm state
src 0.0.0.0 dst 0.0.0.0
	proto esp spi 0x00000000 reqid 0 mode transport
	replay-window 0
	output-mark 0x6/0xab
	auth-trunc digest_null 0x30 0
	enc ecb(cipher_null)
	anti-replay context: seq 0x0, oseq 0x0, bitmap 0x00000000
	sel src 0.0.0.0/0 dst 0.0.0.0/0

Signed-off-by: Antony Antony <antony@phenome.org>
Signed-off-by: David Ahern <dsahern@gmail.com>