removed USM_{AUTH,PRIV}_PROTO_*_LEN macros

The USM_*_PROTO_*_LEN constant macros removed in 329a9d3c9 are used in other
programs using Net-SNMP libraries. I noticed a problem building PHP against
5.8.rc1 but looking at codesearch.debian.net I find a few other programs
that will be affected too: openvas-libraries, zabbix, openhpi, cacti-spine.

/usr/obj/ports/php-5.6.36/php-5.6.36/ext/snmp/snmp.c:1269:29: error: use of undeclared identifier 'USM_AUTH_PROTO_MD5_LEN'
                s->securityAuthProtoLen = USM_AUTH_PROTO_MD5_LEN;
                                          ^
/usr/obj/ports/php-5.6.36/php-5.6.36/ext/snmp/snmp.c:1272:29: error: use of undeclared identifier 'USM_AUTH_PROTO_SHA_LEN'
                s->securityAuthProtoLen = USM_AUTH_PROTO_SHA_LEN;
                                          ^
/usr/obj/ports/php-5.6.36/php-5.6.36/ext/snmp/snmp.c:1287:29: error: use of undeclared identifier 'USM_PRIV_PROTO_DES_LEN'
                s->securityPrivProtoLen = USM_PRIV_PROTO_DES_LEN;
                                          ^
/usr/obj/ports/php-5.6.36/php-5.6.36/ext/snmp/snmp.c:1291:29: error: use of undeclared identifier 'USM_PRIV_PROTO_AES_LEN'
                s->securityPrivProtoLen = USM_PRIV_PROTO_AES_LEN;
                                          ^

Would it be correct to change the above to use these, respectively?

OID_LENGTH(usmHMACMD5AuthProtocol)
OID_LENGTH(usmHMACSHA1AuthProtocol)
OID_LENGTH(usmDESPrivProtocol)
OID_LENGTH(usmAESPrivProtocol)


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