require at least libnmsg6 0.15.1

Dependency on libnmsg package requires 0.15.1 so it looks in this same
plugins directory by default.

debian/changelog

@@ -3,9 +3,10 @@ sie-nmsg (1.2.1-1) debian-farsightsec; urgency=medium
   * Several unit tests added.
 
   * Debian packaging build with compat level 9 so installed library
-    module is in an architecture directory.
+    module is in an architecture directory. Dependency on libnmsg package
+    requires 0.15.1 so it looks in this same plugins directory by default.
 
- -- Farsight Security, Inc. <[email protected]>  Tue, 07 Jan 2020 10:55:04 -0500
+ -- Farsight Security, Inc. <[email protected]>  Wed, 29 Jan 2020 17:23:44 +0000
 
 sie-nmsg (1.2.0-1) debian-farsightsec; urgency=medium
 

debian/control

@@ -47,7 +47,7 @@ Description: Transitional dummy package for migration to nmsg-msg-module-sie
 
 Package: nmsg-msg9-module-sie
 Architecture: any
-Depends: ${misc:Depends}, ${shlibs:Depends}
+Depends: ${misc:Depends}, ${shlibs:Depends}, libnmsg6 (>= 0.15.1)
 Description: SIE message module plugin for libnmsg
  This package extends the libnmsg runtime to support the following
  message types: