ipvs: add static and read_mostly attributes

ip_vs_conn_tab_bits & ip_vs_conn_tab_mask are static to
ipvs/ip_vs_conn.c

ip_vs_conn_tab_size, ip_vs_conn_tab_mask, ip_vs_conn_tab [the pointer],
ip_vs_conn_rnd are mostly read.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Simon Horman <horms@verge.net.au>