REORG: server-state: Move functions to deal with server-state in its own file

All functions dealing with the server-state files are moved to
server_state.c.

srv_update_state() function was renammed to srv_state_srv_update().
diff --git a/Makefile b/Makefile
index d5c3f4c..77960ba 100644
--- a/Makefile
+++ b/Makefile
@@ -877,7 +877,8 @@
         src/ebimtree.o src/uri_auth.o src/freq_ctr.o src/ebsttree.o            \
         src/ebistree.o src/auth.o src/wdt.o src/http_acl.o                     \
         src/hpack-enc.o src/hpack-huff.o src/ebtree.o src/base64.o             \
-        src/hash.o src/dgram.o src/version.o src/fix.o src/mqtt.o src/dns.o
+        src/hash.o src/dgram.o src/version.o src/fix.o src/mqtt.o src/dns.o    \
+        src/server_state.o
 
 ifneq ($(TRACE),)
 OBJS += src/calltrace.o