ipvs: add __aquire/__release annotations to ip_vs_info_seq_start/ip_vs_info_seq_stop

This teaches sparse that the following are not problems:

make C=1
  CHECK   net/ipv4/ipvs/ip_vs_ctl.c
net/ipv4/ipvs/ip_vs_ctl.c:1793:14: warning: context imbalance in 'ip_vs_info_seq_start' - wrong count at exit
net/ipv4/ipvs/ip_vs_ctl.c:1842:13: warning: context imbalance in 'ip_vs_info_seq_stop' - unexpected unlock

Acked-by: Sven Wegener <sven.wegener@stealer.net>
Acked-by: Julius Volz <juliusv@google.com>
Signed-off-by: Simon Horman <horms@verge.net.au>