openssl: configure with --openssldir=/etc/ssl

BSDmakefile passed --openssldir=etc.  A relative openssldir is taken
relative to the prefix, so the generated files described /usr/etc.
FreeBSD has always used /etc/ssl (OPENSSLDIR in
secure/lib/libcrypto/Makefile.common), so configure with that.

Regenerate tools/c_rehash, the only committed generated file that
depends on openssldir.  It is not installed.  No compiled code changes.

Reviewed by:	ngie, markj
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D60396

crypto/openssl/BSDmakefile

@@ -46,7 +46,7 @@ configure:
 	    enable-ec_nistp_64_gcc_128 \
 	    enable-ktls \
 	    enable-sctp \
-	    --openssldir=etc \
+	    --openssldir=/etc/ssl \
 	    --prefix=/usr)
 
 all: patch

crypto/openssl/tools/c_rehash

@@ -12,7 +12,7 @@
 # Perl c_rehash script, scan all files in a directory
 # and add symbolic links to their hash values.
 
-my $dir = "etc";
+my $dir = "/etc/ssl";
 my $prefix = "/usr";
 
 my $errorcount = 0;