Backport a memory leak upstream net-snmp patch (c6facf2f080c9e1ea803e4884dc92889ec83d990) 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/c6facf2f080c9e1ea803e4884dc92889ec83d990/
• Valgrind output:

17,328 bytes in 361 blocks are definitely lost in loss record 696 of 704
at 0x4C29BE3: malloc (vg_replace_malloc.c:299)
by 0x52223B7: CRYPTO_malloc (in /usr/lib64/libcrypto.so.1.0.2k)
by 0x52DDB06: EVP_MD_CTX_create (in /usr/lib64/libcrypto.so.1.0.2k)
by 0x4E9885D: generate_Ku (keytools.c:186)
by 0x40171F: asynchronous (leaktest.c:276)
by 0x400FE7: main (leaktest.c:356)