Why do you bump PORTREVISION here?
Since the patch fixes build in some cases (using security/libressl*) and doesn't change anything else, it's needless.

Since 9.x is nearing EOL, I plan to remove this entry with the next update, so I believe it's not necessary to change it, however if you insist on doing this, I don't mind.

I'm never confident when I need to increment the PORTREVISION, then when I've got a doubt I update it.
But here I'm in the case: "Examples of changes which do not require a PORTREVISION bump. Build fixes which cause a package to become compilable where it was previously failing.", then like you say, it's useless.

I was just trying to push the more "clean" possible port for increase my chance to pass the mentors filter :-)

Setting DEFAULT_VERSIONS from a port is impoper. Use this construct in stead

.if ${SSL_DEFAULT} == base
IGNORE_FreeBSD_9=      Requires newer OpenSSL (set DEFAULT_VERSIONS+=ssl=openssl)
 .endif

Please append the additional check rather than prepending it. Makes the diff easier to understand

-#if OPENSSL_VERSION_NUMBER < 0x10100000L
+#if OPENSSL_VERSION_NUMBER < 0x10100000L || defined(LIBRESSL_VERSION_NUMBER)

Since 9-STABLE is now EOL, this whole .if block may be removed now.