CLEANUP: ssl/server: move ssl_sock_set_srv() to srv_set_ssl() in server.c

CLEANUP: ssl/server: move ssl_sock_set_srv() to srv_set_ssl() in server.c

This one has nothing to do with ssl_sock as it manipulates the struct
server only. Let's move it to server.c and remove unneeded dependencies
on ssl_sock.h. This further reduces by 10% the number of includes of
opensslconf.h and by 0.5% the number of compiled lines.