Cleanup makefile library dependencies of mod_snmp

Calling out to net-snmp-config --agent-libs causes transitive
dependencies to get pulled in, but we don't need those -- a sensible
dynamic linker pulls those in automatically.  Trying to track the
transitive dependencies manually would be a losing battle.

People were recently hitting this on Debian sid/jessie, where libpci
is in the transitive dependency list but isn't otherwise one of our
build dependencies.

src/mod/event_handlers/mod_snmp/Makefile.am

@@ -4,5 +4,5 @@ MODNAME=mod_snmp
 mod_LTLIBRARIES = mod_snmp.la
 mod_snmp_la_SOURCES  = mod_snmp.c subagent.c
 mod_snmp_la_CFLAGS   = $(AM_CFLAGS) `net-snmp-config --cflags`
-mod_snmp_la_LIBADD   = $(switch_builddir)/libfreeswitch.la
-mod_snmp_la_LDFLAGS  = -avoid-version -module -no-undefined -shared `net-snmp-config --agent-libs`
+mod_snmp_la_LIBADD   = $(switch_builddir)/libfreeswitch.la -lnetsnmpmibs -lnetsnmpagent -lnetsnmp
+mod_snmp_la_LDFLAGS  = -avoid-version -module -no-undefined -shared