BUILD: proxy: Missing header inclusion for quic_transport_params_init()

Since this commit:
144289b45 ("REORG: move init_default_instance() to proxy.c and pass it the defproxy pointer")
as quic_transport_params_init() has been moved from cfgparse.c to proxy.c this
latter source file must include xprt_quic.h header.

Should fix #1153 issue.
diff --git a/src/proxy.c b/src/proxy.c
index de66140..745d6ee 100644
--- a/src/proxy.c
+++ b/src/proxy.c
@@ -47,6 +47,7 @@
 #include <haproxy/task.h>
 #include <haproxy/tcpcheck.h>
 #include <haproxy/time.h>
+#include <haproxy/xprt_quic.h>
 
 
 int listeners;	/* # of proxy listeners, set by cfgparse */