CLEANUP: build: rename some build macros to use the USE_* ones

We still have quite a number of build macros which are mapped 1:1 to a
USE_something setting in the makefile but which have a different name.
This patch cleans this up by renaming them to use the USE_something
one, allowing to clean up the makefile and make it more obvious when
reading the code what build option needs to be added.

The following renames were done :

 ENABLE_POLL -> USE_POLL
 ENABLE_EPOLL -> USE_EPOLL
 ENABLE_KQUEUE -> USE_KQUEUE
 ENABLE_EVPORTS -> USE_EVPORTS
 TPROXY -> USE_TPROXY
 NETFILTER -> USE_NETFILTER
 NEED_CRYPT_H -> USE_CRYPT_H
 CONFIG_HAP_CRYPT -> USE_LIBCRYPT
 CONFIG_HAP_NS -> DUSE_NS
 CONFIG_HAP_LINUX_SPLICE -> USE_LINUX_SPLICE
 CONFIG_HAP_LINUX_TPROXY -> USE_LINUX_TPROXY
 CONFIG_HAP_LINUX_VSYSCALL -> USE_LINUX_VSYSCALL
diff --git a/src/connection.c b/src/connection.c
index 908d098..4b4a314 100644
--- a/src/connection.c
+++ b/src/connection.c
@@ -694,7 +694,7 @@
 						goto bad_header;
 					break;
 				}
-#ifdef CONFIG_HAP_NS
+#ifdef USE_NS
 				case PP2_TYPE_NETNS: {
 					const struct netns_entry *ns;
 					ns = netns_store_lookup((char*)tlv_packet->value, tlv_len);
@@ -1228,7 +1228,7 @@
 	}
 #endif
 
-#ifdef CONFIG_HAP_NS
+#ifdef USE_NS
 	if (remote && (remote->proxy_netns)) {
 		if ((buf_len - ret) < sizeof(struct tlv))
 			return 0;