net-snmp: Fix host contamination
If "/usr/local/ssl/include" directory exists on the host machine,
net-snmp will also search the host openssl headers:
x86_64-wrs-linux-libtool: compile: x86_64-wrs-linux-gcc ...
-I/usr/local/ssl/include
Fix this by selecting the proper sysroot headers using
--with-openssl=${STAGING_EXECPREFIXDIR}
Signed-off-by: Changqing Li <changqing.li@windriver.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>