netfilter: ipvs: Add configurations of Maglev hashing

To build the maglev hashing scheduler, add some configuration
to Kconfig and Makefile.

 - The compile configurations of MH are added to the Kconfig.

 - The MH build rule is added to the Makefile.

Signed-off-by: Inju Song <inju.song@navercorp.com>
Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>