security/libressl: Update to 2.3.4

• Upstream marked the 2.3 branch as stable
• Bump SHLIB_VERSION in bsd.openssl.mk
• Note SHLIB_VERSION bump and SSLv3 removal in UPDATING
• Add TLS-enabled netcat binary
• Fix linking issues with MySQL 5.7 [1]
• Includes vulnerability fixes [2]

PR: 208759 [1]
Security: 01d729ca-1143-11e6-b55e-b499baebfeaf [2]
Reviewed_by: feld (mentor), koobs (mentor)
Approved by: feld (mentor, ports-secteam)
Differential Revision: D5902