Fix broken STARTTLS when SharedMemoryKey is enabled.

OpenSSL 1.1 API patch for sendmail had a bug which
prevented sm_RSA_generate_key() function from working.
This function is used to generate a temporary RSA key
for a shared memory region used for TLS processing.
Note that 12.0 and 12.1-RELEASE include this bug.

This affects only if SM_CONF_SHM compile-time
option (enabled by default) and SharedMemoryKey
run-time option (not enabled by default) in a .cf file are
specified. The latter corresponds to confSHARED_MEMORY_KEY in
a .mc file.

PR: 242861
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D23734