netsnmp: Remove ldconfig calls

ldconfig breaks links created by gpu-viv-bin-mx6q.

fixes
http://autobuild.buildroot.net/results/ab5/ab57dd3729d529366808cbfc802f49360b2ec2b9/



[Peter: use NETSNMP_INSTALL_*_OPT, only install initscript for sysv init]
Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Tested-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>