MINOR: args: add new context for servers

We'll have to support fetch expressions and args on server lines for
"usesrc", "usedst", "sni", etc...
diff --git a/src/sample.c b/src/sample.c
index 330f08a..6088869 100644
--- a/src/sample.c
+++ b/src/sample.c
@@ -1125,6 +1125,7 @@
 		case ARGC_RDR: where = "in redirect format string in"; break;
 		case ARGC_CAP: where = "in capture rule in"; break;
 		case ARGC_ACL: ctx = "ACL keyword"; break;
+		case ARGC_SRV: where = "in server directive in"; break;
 		}
 
 		/* set a few default settings */