decode RIPv2 authentication up to RFC4822

decode RIPv2 authentication up to RFC4822

This change addresses a few issues in rip_entry_print_v2() and
rip_print():

1. In the case of Simple Password (RFC2453) authentication the last
(16th) character of a password was never printed. Other password
characters were printed regardless of existing isprint() test.

2. In the case of Cryptographic (RFC4822) authentication there were no
details available for fixed-size auth header and variable-size auth
trailer.

3. Depending on particular hash function used, a normal authentication
trailer "RTE" may be 20 or more bytes long. Iteration over packet RTEs
should stop once a trailer is decoded. Exact number of RTEs in a message
cannot be told from message size any more.

Test cases are added for Request and Response messages with Simple
Password, Keyed-MD5, HMAC-SHA-1, HMAC-SHA-256, HMAC-SHA-384 and
HMAC-SHA-512 authentication modes. Earlier test case is updated to match
new "number of routes" output format.