BUG/MINOR: use the same check condition for server as other algorithms

BUG/MINOR: use the same check condition for server as other algorithms

Such load balance algorithms as roundrobin, leastconn and first will check the
server after being selected with the following condition:
	if (!s->maxconn || (!s->nbpend && s->served < srv_dynamic_maxconn(s)))

But static-rr uses the different one in map_get_server_rr()  as below:
	if (!srv->maxconn || srv->cur_sess < srv_dynamic_maxconn(srv))
After viewing this difference, it is a better choice for static-rr to use the
same check condition as other algorithms.

This change will only affect static-rr. Though all hash algorithms with type
map-based will use the same server map as static-rr, they call another function
map_get_server_hash() to get server.

Signed-off-by: Godbach <nylzhaowei@gmail.com>