Backport a memory leak upstream net-snmp patch (67726f2a74007b5b4117fe49ca1e02c86110b624) into Red Hat Enterprise Linux 7

Issue

• We found the following memory leak in net-snmp library, and upstream committed the patch for the bug.
• Please backport it into Red Hat Enterprise Linux 7.
• Upstream URL: https://sourceforge.net/p/net-snmp/code/ci/67726f2a74007b5b4117fe49ca1e02c86110b624/
• Valgrind output:

==1069== 3,456 bytes in 72 blocks are definitely lost in loss record 1,568 of 1,616
==1069== at 0x4C29BE3: malloc (vg_replace_malloc.c:299)
==1069== by 0x70A63B7: CRYPTO_malloc (in /usr/lib64/libcrypto.so.1.0.2k)
==1069== by 0x7161B06: EVP_MD_CTX_create (in /usr/lib64/libcrypto.so.1.0.2k)
==1069== by 0x4EA3017: sc_hash (in /usr/lib64/libnetsnmp.so.31.0.2)
==1069== by 0x4EA1CD8: hash_engineID (in /usr/lib64/libnetsnmp.so.31.0.2)
==1069== by 0x4EA1DEC: search_enginetime_list (in /usr/lib64/libnetsnmp.so.31.0.2)
==1069== by 0x4EA2256: set_enginetime (in /usr/lib64/libnetsnmp.so.31.0.2)
==1069== by 0x4EC495E: usm_process_in_msg (in /usr/lib64/libnetsnmp.so.31.0.2)
==1069== by 0x4EC58CA: usm_secmod_process_in_msg (in /usr/lib64/libnetsnmp.so.31.0.2)
==1069== by 0x4E7B91D: snmpv3_parse (in /usr/lib64/libnetsnmp.so.31.0.2)
==1069== by 0x4E7C1F6: ??? (in /usr/lib64/libnetsnmp.so.31.0.2)
==1069== by 0x4E7CE94: ??? (in /usr/lib64/libnetsnmp.so.31.0.2)