Fix the following -Werror warning from clang 10.0.0 in bsnmpd:

Fix the following -Werror warning from clang 10.0.0 in bsnmpd:

usr.sbin/bsnmpd/modules/snmp_pf/pf_snmp.c:1661:4: error: misleading indentation; statement is not part of the previous 'else' [-Werror,-Wmisleading-indentation]
                        return (-1);
                        ^
usr.sbin/bsnmpd/modules/snmp_pf/pf_snmp.c:1658:5: note: previous statement is here
                } else
                  ^

The intent was to group the return statement with the previous syslog()
call.

MFC after:	3 days