David Goulet authored Aug 23, 2018 and Nick Mathewson committed Aug 29, 2018

The OpenSSL "RSA" object is currently 408 bytes compares to the ASN.1 encoding
which is 140 for a 1024 RSA key.

We save 268 bytes per descriptor (routerinfo_t) *and* microdescriptor
(microdesc_t). Scaling this to 6000 relays, and considering client usually
only have microdescriptors, we save 1.608 MB of RAM which is considerable for
mobile client.

This commit makes it that we keep the RSA onion public key (used for TAP
handshake) in ASN.1 format instead of an OpenSSL RSA object.

Changes is done in both routerinfo_t and microdesc_t.

Closes #27246

Signed-off-by: David Goulet <dgoulet@torproject.org>