snmppp: fix legal informations after version bump

Fixes:

  http://autobuild.buildroot.org/results/e64/e64c3edcb00132620b07ad815c6e4d33b70c262f/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/snmppp/snmppp.mk

@@ -12,6 +12,6 @@ SNMPPP_INSTALL_STAGING = YES
 # no configure script in tarball
 SNMPPP_AUTORECONF = YES
 SNMPPP_LICENSE = SNMP++
-SNMPPP_LICENSE_FILES = snmp_pp/snmp_pp.cpp
+SNMPPP_LICENSE_FILES = src/v3.cpp
 
 $(eval $(autotools-package))